Acts 2:38

Peter said to them. They have already declared their faith in Christ (Acts 2:37). Now, for the very first time, the terms of pardon under the New Covenant will be announced. Peter will tell them how to reach out through faith to seize the sacrifice of Christ and make themselves part of it. Turn away from your sins. That is, repudiate what you have done. Turn away from sin, and turn to God. [The technical term is; repent.] And be baptized. This act is a visible demonstration of both faith and turning from sin. [Repentance is a change of mind: baptism is a change of state.] In the name of Jesus Christ. By his authority. Without his authority, it would be only "water baptism." With his authority, it becomes the new birth of John 3:5. So that your sins will be forgiven. This is the promise. When their faith became real through turning from sin and being baptized in the name of Jesus, they would be forgiven for their sins, including the sin of killing Jesus. The promise of forgiveness is to all who comply with these terms of salvation. And you will receive God's gift, the Holy Spirit. McGarvey says the meaning here is the Holy Spirit as a gift. The world cannot receive this Helper. [Note that here, the gift of the Spirit comes in connection with baptism. That is, forgiveness of sins and the Spirit as a gift, are two results of turning from sin and being baptized. See notes on Matthew 28:19-20; Romans 6:1-11; John 7:38-39.]