36 “Therefore let all the house of Israel know for certain that God has made Him both Lord and Christ — this Jesus whom you crucified.”
37 Now when they heard this, they were pierced to the heart, and said to Peter and the rest of the apostles, “Brethren, what shall we do?”
38 Peter said to them, “Repent, and each of you be baptized in the name of Jesus Christ for the forgiveness of your sins; and you will receive the gift of the Holy Spirit. 39 For the promise is for you and your children and for all who are far off, as many as the Lord our God will call to Himself.”
40 And with many other words he solemnly testified and kept on exhorting them, saying, “Be saved from this perverse generation!”
41 So then, those who had received his word were baptized; and that day there were added about three thousand souls.
The key to the passage is 38-39, yet those are the very ones which many misunderstand apply.
“Repent, and each of you be baptized in the name of Jesus Christ for the forgiveness of your sins; and you will receive the gift of the Holy Spirit. For the promise is for you and your children and for all who are far off, as many as the Lord our God will call to Himself.”
Note that when they hear the Law (“this Jesus whom you crucified”), they respond in despair: “what shall we do?” Quite often, Peter’s response is seen as directing to more Law… “do this!” But is that what the text says?
Everything that is mentioned is a gift given to them, not something they offer (repentance, baptism, forgiveness, promise). The key then is that Peter points them to the Gospel — baptism is God’s work (something done to them) and gift, providing forgiveness of sins and the Holy Spirit. Further, he states that the “promise is for …”
Thus, far from being a Law response to someone under the Law, Peter gives a Gospel response, the only thing that cures despair and hopelessness, along with sin and death. Peter proclaims Jesus Christ to bring life to those who had none.
And that is the Easter hope and what the celebration is all about.