Photo by, Hajor.
Peter's first sermon took place in the porch of the temple. This was where everyone would go to pray each morning and evening. It was the perfect spot to preach because thousands of people came by every day.
After his sermon, Peter said,
“Therefore let all Israel be assured of this: God has made this Jesus, whom you crucified, both Lord and Messiah.”
When the people heard this, they were cut to the heart and said to Peter and the other apostles, “Brothers, what shall we do?”
Peter replied, “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. The promise is for you and your children and for all who are far off—for all whom the Lord our God will call.”
With many other words he warned them; and he pleaded with them, “Save yourselves from this corrupt generation.” Those who accepted his message were baptized, and about three thousand were added to their number that day. Acts 2:36-41
The reason I underlined the words above is because something really struck me when Peter later gave a sermon to the rulers of the people. They were jealous of the disciple's influence and had them all arrested. They told the disciples to quit preaching in Jesus' name.
Peter said, "We must obey God rather than human beings! The God of our ancestors raised Jesus from the dead—whom you killed by hanging him on a cross. God exalted him to his own right hand as Prince and Savior that he might bring Israel to repentance and forgive their sins. We are witnesses of these things, and so is the Holy Spirit, whom God has given to those who obey him.”
"But when they heard this, they were cut to the heart, and wanted to kill them." Acts 5:29-33
Paul used the same words in his sermon. He accused both the people and the rulers of killing Jesus. The common people reacted with sorrow and shame. They repented and were baptized.
The rulers reacted with hatred and murderous thoughts. I think they would have killed the apostles that very day if Gamaliel had not stopped them.
My sister once asked me why it says in the Bible that God hardened Pharaoh's heart. (Exodus 11:10) She knew the Bible, and this did not agree with the rest of Scripture.
I told her about what I had read. God is like the sun. The sun hardens clay but it melts butter. Hearing about God will either harden a person or soften a person.
It is up to each human in the world to make a decision about God. He will either make you angry, completely indifferent or he will melt your heart.