Acts 2:37-39

37 When they heard this, they were pierced to the heart and said to Peter and the rest of the apostles: “Brothers, what must we do?”
38 “Repent,” Peter said to them, “and be baptized, each of you, in the name of Jesus the Messiah for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. 39 For the promise is for you and for your children, and for all who are far off, as many as the Lord our God will call.”

Peter shared the good news of Jesus Christ, Savior and Lord. He shared the need of man who in his sin and rebellion against God has brought upon himself the judgment of God. That each of us is responsible for the death of Christ, for it was our sin that sent him to the cross. But that God did not leave him in the grave, but raised him from the dead that he might offer us the promise of forgiveness of sins and eternal life with him. Now man must respond to that offer. “What shall we do?”

Repent. The message of Jesus Christ is that we must repent. That means that we must turn from our former way of acting and thinking and turn toward God’s way of acting and thinking. It is a change of intellect, emotion and volition. We change the way we think, the way we react and what we do. Peter’s message is the same as John the Baptist’s and Jesus’. Repentance involves a change in approach to life. It includes an new and intense abhorrence of sin and an adherence to Jesus.

It is the message to the world, we must change the way we have lived in, reacted to and thought about the world. Christianity is not a religion that can be added to your plate, it is a relationship that will overtake your life. You cannot remain the same as you are today and claim Christ as your Savior and Lord. That is why Peter includes baptism in his statement. Repentance is clearly the emphasis in this urgent command. But baptism is associated closely with repentance for baptism is the visible picture of the inward change. For Peter, it would have been inconceivable that anyone who would repent of their sins and receive Christ as Savior and Lord would not be baptized. Baptism is a natural response for the regenerated Christian. It does not bring forth forgiveness of sins, it accompanies genuine conversion. This is the message Peter brought to the crowd on Pentecost. It is the same message preached for 2000 years and still today.