What does the Bible say about the sermon at Pentecost?

In Acts 2, Peter stands before the crowd after the pouring out of the Holy Spirit and proclaims the gospel, asserting that Jesus, whom they crucified, is both Lord and Christ. He cites the prophet Joel to explain that this event fulfills God's promise to pour out His Spirit, emphasizing the necessity of repentance and belief in Jesus for salvation. This sermon marks the birth of the church as about 3,000 souls were added that day, reflecting the power of God's word when accompanied by His Spirit.