Read Acts 2.
What better way to quickly spread the Gospel throughout the Roman world than this! The Holy Spirit came upon these disciples as Jesus promised. With Jews gathered in Jerusalem for the annual celebration of Pentecost, they heard "the mighty works of God" being proclaimed in their own languages. This unusual event not only gained their attention and drew a crowd, but it provided a platform for Peter to preach the good news about Jesus.
As a nation, Israel had rejected Jesus. The religious leaders of the day claimed Jesus was empowered by Satan. Though the crucifixion was all "according to the definite plan and foreknowledge of God" (v.23), the message presented human responsibility in no uncertain terms. "This Jesus whom you crucified" (v.36). Jesus taught in John 16 that the Holy Spirit would convict of sin. "Now when they heard this they were cut to the heart" (v.37).
It is one thing to feel the pang of sin. It is quite another to desire to resolve the problem. When these listeners heard the message and were pricked in their conscience, they responded: "Brothers, what shall we do?"
The good news of Jesus is that forgiveness and life-change is available to all. The remainder of this chapter provides an outline of what is required by all who desire to have eternal life and then to grow as a child of God. What Peter said was in exactly the Lord's command in Matthew 28:18-20.
The word means to turn. It requires one to admit they have gone in the wrong direction and sinning against God. Then, realizing that Jesus died for our sins, one must turn to the Lord for forgiveness. That repentance saves one from eternal judgment and births them into the family God.
2. Be baptized.
This is the New Testament means of outwardly and publicly declaring one's faith in Jesus. There is no power in the water. Being let down into the water and raised back up, symbolizes what took place already on the inside. It is a picture of the death of the old self and that God has made that one a new creation in Christ Jesus (2 Corinthians 5:17).
3. The gift of the Holy Spirit.
At the moment of salvation in Jesus, "you will receive the gift of the Holy Spirit". He takes up permanent residence in the life of the believer. He is the seal and guarantee of our eternal life (Ephesians 1:13-14). He affirms that we belong to Christ. "Anyone who does not have the Spirit of Christ does not belong to him" (Romans 8:9b).
4. Added to the fellowship.
When a person was saved and baptized, they became an official part of the congregation of believers in Jerusalem. The New Testament knows nothing about "lone ranger" Christians. True believers gladly engage themselves in a committed body of believers for the purpose of mutual growth and service. Without this, one will never grow up spiritually and be all that God has designed that person to be.