From the ESV:

And Peter said to them, “Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit.”

This passage has long been used by those who wish to prove baptismal regeneration to show that both repentance and baptism are necessary for sins to be forgiven.  Those who argue against this interpretation have done so ingeniously and in several different veins:

• The word translated for can mean just as easily mean “because of,” rendering the passage “Be baptized because of the forgiveness of your sins.”
• This passage is unclear whereas heaps of other passages clearly fall on the side of “salvation by grace through faith.”  (See Ephesians 2:8-10, John 3:16, Romans 10:9-13, etc.)
• Those who are being addressed are already “saved” in that they awaited the coming Messiah and are now having their faith actualized by Peter’s sermon of the crucified Christ.

Each of these is a noble effort and may very well be the correct exegesis of the passage, but there is an historical problem that has escaped many: namely, that the earliest proponents of infant baptism (men like Augustine and Pope Innocent I) never used this as a scriptural argument for baptismal regeneration!  Only after the idea that original sin must be washed away by baptism came on the scene did infant baptism even rear its ugly head.  Not until the Campbellite movement of the 1820s does Acts 2:38 find its way into regular baptismal regeneration discussions.

So why did early proponents of the practice not utilize such a seemingly strong verse for their cause?  Though it has been established that many of the western Patristic theologians had only a rudimentary understanding of Greek, it may be in that original language that the answer lies.

Before we look at the text, remember two rules of Greek: 1) as it is an inflected language, word order means almost nothing, and 2) pronouns and their antecedents (just like nouns and their modifiers) must agree in gender and number. 

Drawing from Rule #2, the word for “Repent” is a second person plural imperative that should be understood as “You all repent.”  Then we switch to singular language: “let each of you be baptized.”  The final phrase of import, “for the forgiveness of your sins,” refers to a plural second person and is grammatically tied to “Repent.”  This can be confusing because the English second person is the same in singular (sg) and plural (pl) so that I can say to my friends Josh and Rosie, “I love your kids” without any confusion as to the identity of “your.”  The kids are not Josh’s or Rosie’s but Josh’s and Rosie’s.  The “your” is plural.  The Greeks solved this by having different endings for the singular and plural second person so that there is no ambiguity in the Greek.

Thus, drawing from Rule #1 that word order is essentially irrelevant, there is no problem translating the phrase into English in a way that more correctly reflects the grammatical relationships:

And Peter said to them, “Repent (pl) for the forgiveness of your (pl) sins,” and he said, “Let each (sg) of you be baptized (sg) in the name of Jesus Christ, and you all (pl) will receive the gift of the Holy Spirit.”

This device is called an intercalation and is used elsewhere in Scripture such as in Ephesians 4:26-27:

Be angry, but do not sin: let not the sun go down on your wrath: and do not give the devil an opportunity.

Here the first and third phrases contain second person imperatives while the middle phrase contains a third person imperative.  This ABA structure is used also in Mark 3:19-35, 5:22-43, 11:12-21, 12:38-13:2, 14:66-72, and John 18:13-27.  Think of it like a sandwich – the pieces of bread are very much the same, but the meat is in the middle.  Thus, for the Greek hearer, the shift in number or person draws attention to the words as being the most important part of the commandment.

Returning to Acts 2:38, given that we have already established the logical flow of the phrases, this new knowledge of intercalations also allows us to know for certain Peter’s main message.  While “Repent for the forgiveness of your sins” is important, it is clear in the context of Acts 2 that these men were already in a receptive state for repentance.  Thus, Peter’s desire is that these men be baptized – each of them – to complete the conversion process begun in repentance.

It is ironic that we Baptists have become baptizophobic.  So staunch are we on salvation by grace alone through faith alone and so scared are we of the Campbellite error that we have divorced baptism from the process of conversion.  I challenge anyone to point to a fully orbed conversion in Scripture – apart from the special case of the thief on the cross – that does not prominently include baptism.  There will be many unbaptized people in heaven, but there is no such thing as an obedient convert to Christ who has not gone through the baptismal waters.

(Special thanks to Kirk R. MacGregor in A Molinist-Anabaptist Systematic Theology for the meat of this post.)