That statement might seem harsh until you read the entire sermon given by Peter (Acts 2:14-36). The effectiveness of God’s Word through this apostle is evident in the response; “Now when they heard this they were cut to the heart, and said to Peter and the rest of the apostles, “Brothers, what shall we do?”” (2:37). The conviction God brought to those listening was not a mental exercise, but a ‘cutting of the heart’. This is what the Word of God should be doing when it is preached in the power of the Holy Spirit.
Their question, “what shall we do?” shows they were not satisfied just to feel conviction, but the conviction in their hearts demanded action, a change of life. The Word of God and the Spirit of God in preaching the gospel will not leave us as we were. There must be transformation! Peter answers their question; “And Peter said to them, “Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit” (2:38).
True repentance causes those hearing to identify immediately through baptism with the Person who saved them from sin and hell. Receiving the Holy Spirit is the immediate, God-given power to live transformed in a new relationship with God through His Son, Jesus Christ. Anything less is powerless and leaves persons where they were.