The setting: Peter has just preached a powerful, Spirit-led message to a large crowd at Pentecost in Acts chapter 2. Immediately following his message, the people were convicted and asked a pressing question. Peter responded with a direct answer to that specific question.
The main idea of Peter’s message was that Jesus was the true Son of God, and many of the Jews there had, at the very least, tacitly approved of His crucifixion. All authority in heaven and on earth had been given to Jesus, and He was sitting at the right hand of the Father. He is still there. This is His rightful place as Deity, an honored Person of the godhead. He was, and is, Lord and Christ. The blood, shed because of the sacrificial love and grace of Jesus, the atonement, was now their only hope. We know that the Law could not save.
So the people were powerfully convicted by Peter’s message, and they asked what they must do. Context becomes important here in verse 37. We must make an inference about what the question meant and place something in brackets to fully understand the question. Will we fill in the blank here with the proper contextual question? Will we conclude that the question referred to actions required because of their desire to receive salvation? Or, will we conclude that they had just received salvation and wanted to know what to do next?
Since Peter did not speak to them anywhere in this text about an outward sign of an inward change, it would be most logical to conclude that the people were interested in knowing what they should do in order to receive salvation. This is the proper context.
If you say that Acts 2:38 refers only to a response after salvation, the question in verse 37 seems a bit dramatic, implying that something needs to be done immediately even though salvation has already occurred. Does that make sense? I don’t think a post-salvation action would have prompted this feeling that something serious was about to happen, this sense of the anticipation of change. “What must we do?” The question gives us a hint of desperation/urgency and that some kind of transition is impending. So if we add a bracket for clarification, it must read, “What must we do [in order to be saved]?” Also “and you shall receive the gift of the Holy Spirit” seems to be a direct result of what’s just happened in verse 38. Does the Holy Spirit initially indwell us post-salvation?
There are people today who would say this was a post-salvation question and would also now tell you that you can wait for an extended period of time to be baptized after you believe in Jesus (i.e., 2 or 3 weeks later during a monthly or quarterly ceremonial service). No hurry, right?–no critical timing involved. This delay does not square with Bible teachings. Should we also allow for delayed repentance (considering what Acts 2:38 says about repentance and baptism)?
Context here definitely would lean heavily toward the idea that the word for (eis) in “for the forgiveness of sins” means “leading unto,” NOT “because of.” See 1 Peter 3:21 and Luke 13:3 for the essential purposes of baptism and repentance. God bless you in your studies.