A question that comes up a lot in discussions of infant baptism, is "why do you do it?" The question behind the question, of course, is "are you teaching that a child is saved by baptism?"
This is of particular concern to people who are many stages removed from Roman Catholicism. Anabaptists and their modern descendants viewed the lingering practice of infant baptism as a hold-over from Catholicism, something left unreformed by the reformers, particularly Calvin and Luther. To someone with this perspective, the practice of infant baptism has a lot of baggage left over from the Catholic view of it. This can be disconcerting.
This is also a question I have wrestled with and wanted to share my incomplete thoughts on. Fundamentally the answer to my question "why" is "because God said I should". You can see my argument for why I think it is appropriate here. However, this is not the answer most people are looking for. More specifically, they are looking for what function baptism plays in the life of a Christian, particularly an infant Christian.
Defining a Christian
One immediate objection that might come is the question of who "counts" as a Christian. The Bible doesn't really use the term in any technical sense, so we should try to understand what we mean when we use the term. For a lot of people, the definition of a Christian is "a believer". By which they mean "a saved person" or "a regenerate person". However, this is not something that is immediately visible to us. Standing outside the minds of others we do not have access to the salvific status of a particular man or woman. God does not intend us to know this state in any kind of infallible way and does not alter his call on our behavior towards people to be dependent on whether or not they are "believers" in that sense. It should be obvious that he does not call on us to make those sort of discernments because he does not give us the information that would be necessary to make such a discernment.
We are given some criteria by which to judge a person's spiritual state. "By their fruit you will know them" (Mt 7:16). But strictly speaking in context, this is not speaking about trying to determine whether someone is really saved. Rather it is a question of whether we should listen to those people. A life of biblically defined fruit of righteousness and victory over sin is the life of someone to whom we should listen. A life of sin and corruption implies that the person is not a true teacher.
As an aside, it certainly helps you to see that if a person is teaching and you find that they are in serious unrepentant sin, it generally should alert you that there's something off about this person's teaching. A variation of this is in regard to the qualifications for eldership (1 Tim 3, Titus 2). The reason character is so central to the requirements is because that is the fruit of a transformed life. They are able to lead well because their lives demonstrate that they have a relatively accurate view of God and his grace and can therefore be trusted to communicate that view. Of course, we are not "fruit inspectors". There is a version of this sort of thing that could become sinful. We all fall short in many ways (Jas 3:2) and a lack of perfection is not a slight against a person's ability to lead and teach.
Then, what is a biblical "Christian". We could use synonymous terms like "disciple", which essentially is "someone who is following Christ". This does not make any claim about their status regarding election or regeneration. A person may be a temporary follower of Christ, or an unfaithful follower of Christ.
Covenant Membership
Rather, we can ask whether the person is a member of the covenant community of God. We may enter it in the same way that the original covenant community was entered, by "conversion" or by birth. I put conversion in quotes because the conversion in sight (Exo 12:48) does not make any claim to whether they are "really a believer" or not. They are simply participating in the life of the community. They share the meals, they serve their neighbors, they learn to follow God.
Likewise, a child shares our meals, serves their neighbors and learns to follow God from the first day they are born. While this sometimes look like instruction ("no, you may not hit your sister"), they learn also by watching our example. The Father is an image of God the Father, a symbol of God (Gen 2:24; Heb 112:7, 12:9, many others) . The child learns about God by watching their father. They learn about God's action in the church by watching their mother. They learn about Christ's relationship to the church by watching their father and mother's relationship (Eph 5:22-32).
All of this is "teaching" them about God, whether its intentional or not. This should also humble us greatly. If a father mistreats and manipulates his wife, he is teaching the child that Jesus mistreats and manipulates his people. That makes him a false teacher. If a wife disrespects and refuses to submit to her husband, she is teaching that the church should refuse to submit to Christ. That makes her a false teacher. Who is adequate for these things (2 Cor 2:16)?
In this rudimentary sense, we are all "disciples" as we learn about God. However, the Bible doesn't use that term for people who are learning and believing false things about God. We can't make false disciples. In a larger sense in fact, we could say that until we have become "complete in Christ" (Col 1:28) we are still in the process of "being made a disciple". We are to learn to "obey everything [Christ] commanded us" (Mt 28:18-20). So a child is being "made a disciple" as he is being taught true things about God and his church from his godly parents.
I will make the statement that a Christian is best defined as a person who is covenantally united to Christ, though still under the obligation to live out their living faith in order to be "saved". I argued in the above link why I think children are included, but we can say as a shorthand, "because Peter said this is for you and your children in Acts 2:38-39".
Function of Baptism
As I've pointed out before, we can sometimes get ourselves tied up in knots trying to come up with exact, precise, systematic answers to difficult biblical questions. Have you ever read the Chalcedonian definition of what the nature of Christ's divinity and humanity is?
“Therefore, following the holy Fathers, we all with one accord teach men to acknowledge one and the same Son, our Lord Jesus Christ, at once complete in Godhead and complete in manhood, truly God and truly man, consisting also of a reasonable soul and body; of one substance [homoousios] with the Father as regards his Godhead, and at the same time of one substance with us as regards his manhood; like us in all respects, apart from sin; as regards his Godhead, begotten of the Father before the ages, but yet as regards his manhood begotten, for us men and for our salvation, of Mary the Virgin, the God-bearer [theotokos]; one and the same Christ, Son, Lord, Only-begotten, recognized in two natures, without confusion, without change, without division, without separation [en duo phusesin, asungchutos atreptos, adiairetos achoristos]; the distinction of natures being in no way annulled by the union, but rather the characteristics of each nature being preserved and coming together to form one person and subsistence [hupostasis], not as parted or separated into two persons, but one and the same Son and Only-begotten God the Word, Lord Jesus Christ; even as the prophets from earliest times spoke of him, and our Lord Jesus Christ himself taught us, and the creed of the Fathers has handed down to us.”
It's pretty difficult to get your mind around all the details of exactly what this means in practice. Even trying to explain it can easily slide you into heretical territory.
Thus, I think similar things have happened to us in trying to nail down the soteriological details of exactly how all this plays out. People get into arguments over whether regeneration happens before or after faith, but the Bible does not speak plainly about the chronological ordering. This is not to say the discussion isn't worth having or that there isn't a right answer. I would just urge us all to try and speak in Biblical terms and let the mysteries be present before trying to philosophize ourselves to hard and fast conclusions that end up sending us into confusion.
The eagerness to have cold hard answers to these sorts of questions can lead us to wrong conclusions, even if the "answer" we have is correct. Are some people elect? Of course (Rom 8:33). Can the elect rest assured in their election? Well Peter tells us to be "diligent to confirm your... election" (1 Pet 1:10).
Because of the confusion of the jumping to broader conclusions based on answers to systematic theological concerns we get things like "The Private Memoirs and Confessions of a Justified Sinner".
The plot concerns Robert Wringhim, a staunch Calvinist who believes he is guaranteed Salvation and justified in killing those he believes are already damned by God... [It has been interpreted as] a study of religious fanaticism through its deeply critical portrait of the Calvinist concept of predestination.
But the problem is not "predestination", the problem is the view that we can know that we (and others) are (or are not) predestined apart from our behavior in this life. Attempting to arrogate the powers of God to know the future to ourselves regarding the ultimate condemnation or salvation of ourselves or others is specifically preached against by Christ (Mt 7:1, and chapter 13 in the parables of the weeds and the net) and by Paul (Rom 14:4).
Baptism "Saves"
How does this relate to the question of baptism?
Baptism "saves" according to Scripture (1 Pet 3:21). But we know that it is faith that saves (Rom 3:28)! One theological ditch we might fall into is the baptismal regeneration ditch. But then we have to start philosophizing about the timeline and association of faith/regeneration/apostasy and other related issues in order to square the circle that we've just created.
To avoid this, it is best to stick as close to the Bible as you can. How is "salvation" understood in Scripture? If you read that word and hear "justification", you are not doing justice to the multiple layers of meaning that salvation has always had in the Bible. In a sense it is a temporal salvation, a removal of enemies, a rescue from danger. In another sense it is the moment of justification. In another it is the final moment when you pass the judgment of Christ and are "saved" despite your sinfulness. We speak of "salvation" now, but it is an "already, not yet" sort of concept. If we try to collapse it down to the moment of "justification" (which we can't really know exactly when that is anyway for most people) we've deformed the scriptural use of the concept and created a problem passage where none exists.
As put by Hans Fiene on twitter:
When one comes across a perceived contradiction in the Scriptures, it is generally unwise to start off with the assumption that one of the passages doesn't mean what it says, that it MUST be using an alternate definition of one or more of the words involved. So, when we the Bible says we're saved by faith alone and when it says that baptism saves, it is unwise to resolve the tension by saying, of the baptism passage that "saves" doesn't mean what it typically does or that "baptism" doesn't refer to the washing of water in the Triune name as instituted by Christ. It is especially unwise to do this if there is no indication from the author, in the context, that alternate definitions of the words are being used. Taking such a view of Scripture, you see, will render it quite useless...
You are dying. You go to the doctor. He gives you a pill, and says "swallow this and you'll be saved." The doctor saves. The pill saves. Swallowing the pill saves.
What is the mechanism by which we are freed from sin? The Bible gives us some guidance on the topic, but fundamentally it is a work of the Holy Spirit (Gal 5:16, 22, 25). But the Spirit does not always simply act unilaterally. Primarily the Spirit acts through the physical means given to the church. We are not gnostics. The physical movements and actions of the church are in no way dissociated from the genuine spiritual reality of what is happening. When we have communion the Spirit works through the bread and wine and in a sense we "proclaim Christ's death" (1 Cor 11:26). How does this happen? By the power of the Spirit. It does not always have to look specifically like someone shouting out "Christ died for our sins" in the process of communion, nor is that the only level on which this is true. The act itself proclaims. The Spirit intercedes (Rom 8:26-27).
Likewise with baptism, we do not need to be saying "I appeal to God for a good conscience" in baptism to make the reality of that appeal present. Nor is it abundantly clear in Peter's words that it is the person themselves making that appeal. In a sense, the Spirit (through the action of the church) is making the appeal on the behalf of the person being baptized. How exactly does the Spirit use baptism to create the reality of saving and sanctifying work in a person's life? That's a mystery for wiser minds than mine, but it should be sufficient to say that he does.
What we know then is that baptism alone is not sufficient for justification. Justification is by faith, not by works, even the work of baptism. Nor is it necessary for justification, as we know from the thief on the cross (although some understand the darkness of the sun to be intense rain, in which case he was being baptized at that time). What we do know is that it is the sign of the covenant of the promise (Acts 2:38; cf Acts 26:6). We know that the Spirit uses the means he has decreed in his word to do his work.
Then what is the function of baptism? It is a means by which the Spirit imparts the saving work of Christ. I cannot nail it down any more specifically than that. We know that people can be baptized and not justified (Acts 8:13, 23). But the fact that a person who has been washed and sanctified can still persist in unbelief (Heb 10:29) does not make God unfaithful (Rom 3:3, cf 2 Tim 2:11-13). We honor the faithfulness of God in baptism and leave salvation in his hands, putting our faith (trust) in him that he will not be unfaithful to his promises or to his purposes, which we do not question (Rom 9:20).
We also do not by this nullify the mercy of God. Obviously, people are converted as adults, and thus infant baptism is not necessary for a person's eventual justification. However, we could also point out that a parents' instruction in the truth of God is not necessary for a person's salvation because many are converted with ungodly parents. Does that mean that we should not teach our children the truth of God? Of course not! Does that mean that whether a person hears about God from his earliest age or not is entirely irrelevant to whether he eventually has saving faith? Of course not!
Therefore we baptize in faith, as an appeal to God. We teach the truth of God for the same reason. Exactly how all this works together to eventually inculcate faith in the heart of the regenerated "believer" we cannot know exactly.
I think one of the reasons this is hard to accept for some is that we can draw a straight line between "knowing truth about God" and faith, when we think in human terms. But this misunderstands the origin of faith. Faith is not the result of effective persuasion but of the action of the Spirit of God (1 Cor 2:4-5). When we draw that straight line through the logical facilities of a person "old enough to understand the gospel" we are drawing a false line. In fact, the natural man cannot understand or accept the things of the Spirit, including the gospel (1 Cor 2:12-14). The line is crooked, but God makes the crooked path straight.
Concluding Thoughts
It is important that we realize that much of the fabric of reality is not immediately apparent to us. Consider Elisha and the vision of the heavenly host:
2 Kings 6:15 When the servant of the man of God rose early in the morning and went out, behold, an army with horses and chariots was all around the city. And the servant said, “Alas, my master! What shall we do?” 16 He said, “Do not be afraid, for those who are with us are more than those who are with them.” 17 Then Elisha prayed and said, “O Lord, please open his eyes that he may see.” So the Lord opened the eyes of the young man, and he saw, and behold, the mountain was full of horses and chariots of fire all around Elisha.
Does this mean that the army of angels is going to be physically hacking their enemies with invisible fire swords and overrunning them with invisible chariot wheels? No. It just means there is great power arrayed in defense of the city. Elisha calls upon that power to strike them with blindness. While this is a direct miracle, often God chooses to act alongside human action to accomplish his will. This is all over the Old Testament:
2 Chronicles 13:16 The men of Israel fled before Judah, and God gave them into their hand. 17 Abijah and his people struck them with great force, so there fell slain of Israel 500,000 chosen men. 18 Thus the men of Israel were subdued at that time, and the men of Judah prevailed, because they relied on the Lord, the God of their fathers.
Was there a miracle here? Not any that are apparent in the text. However, it's clear that it is the action of God that makes the difference in the battle, not their strategy. This doesn't mean that God didn't use their strategy to accomplish the intention.
We have a major failure to understand the working of the Spirit often times. We tend to think of it like a partnership between two humans, that I do part and that you do a different part. Analogies necessarily fail us here, but we might better understand that the Spirit's working in the innermost parts of reality are reflected as we operate at the level of our own awareness. When we preach the word and the Spirit creates faith in a man, it's not because the logic of it impresses him, but because the Spirit changes his heart. However, that might look like him being impressed by the logic of it. It's just important that we do not get the cart to pull the horse. The Spirit's action is the critical part. No logical arguments without the Spirit's action will be sufficient to create faith.
Thus, with Baptism, we recognize that it is the ordinary means by which a person is included in the New Covenant. The Spirit works through the action, the action is no mere symbol. How exactly does this all work? Not for us to know precisely. We who accept infant baptism will baptize those who profess faith in Christ, along with the households of the faithful. This makes no claim as to who is "saved" or not. It is an act of placing trust in God to be the one that saves through faith. Since God promises to be faithful to the children of the faithful man, and that the child taught in the way he should go will not depart from it, we see this as merely one of many acts that the faithful do to call upon God's promises and save the child. This is no mere guess or blind "hope", but a dependence on the mercy and graciousness of our Lord.
A Side Note on Reductionism
In the study of physics we have tried to explain everything from a basis as low as you can possibly get. However, we have found that once you get "small" enough, you stop interacting with things in ways that make sense to our everyday experience. We start thinking in terms of forces, and distinctions between waves and particles cease to be adequate to explain what we are seeing. The essence of all is, of course, that God holds creation together by the strength of his will more or less directly. We can see this process and even quantify it, but there will always be one more step below that we can go.
This investigation is not useless, but we must recognize that even when you get down to the nitty gritty of electrons and protons and neutrons, when it comes to explaining precisely how all this works together for a person to perform a pole-vault, the connections are not obvious. Maybe it's not impossible to resolve, but we must recognize which level of analysis we are operating on and note that what is explained well at one level of analysis might fall apart if you try to extend it to another. Our less than perfect understanding pretty much guarantees such failures.
Attempting to explain the metaphysical dynamics of how salvation is applied through the action of the Holy Spirit by faith, through baptism, is not something that will be easy to do and get exactly right. At one level of analysis we are saved through faith, apart from works, at another baptism saves. The one does not contradict the other, we may just lack the necessary analytical tools to resolve the apparent tension. The Spirit is what saves, justification is through faith, the Spirit usually operates by what we would consider "mundane" means. The problem tends to be that we fail to realize that there is nothing in the world that is genuinely mundane. Why should sound waves vibrating a piece of skin in your ear have the power to change the way you think? Why should light from pixels on a computer screen do the same? It's all Spirit-driven.
Just because there is no recognizable miracle doesn't mean that the Spirit isn't operating "supernaturally". Just because we do not see anything unusual happening when a person is convinced to give his life to Christ doesn't mean that what was really happening wasn't the replacement of a heart of stone with a heart of flesh.
I would say that the baptism is a means by which the Holy Spirit operates in a person's life. It is generally not coterminous with regeneration, but that does not make it worthless. Saying that baptism doesn't do anything is no different than saying that preaching the gospel doesn't do anything. It's just words, after all. The Spirit is what ultimately changes a person's heart, not the words you spoke or the water you baptized with. That's true enough but it neglects that the Spirit operates through means. Those means are often physical "mundane" actions taken by the people of his church. The reformers understood that an infant makes the baptism effective through faith. That need not be prior to nor alongside the action. We, in a sense, appropriate the promise rendered in baptism through faith.