In Gareth Reese's commentary on Acts, he notes the interesting parallels in the outlines of sermons in the Book of Acts. Here are his words:

The same major points were regularly made by the apostles when preaching to Jewish audiences.

I. An affirmation that the time of the fulfillment of the Old Testament prophecies had come

II. A rehearsal of the ministry, death, resurrection and ascension of Jesus

III. An appeal to the relevant Old Testament Messianic prophecies whose fulfillment in these events are evidence Jesus is himself the Messiah

IV. A call to repentance. (p. 58)

These sermons can be checked for such a theme. In Acts 2, Peter preaches in Jerusalem on Pentecost. He makes use of prophecies from Joel and Psalms, reminds the people of the deeds of Jesus and boldly proclaims his Messiah-ship due to his undeniable resurrection. In Acts 3, Peter preaches in the temple area after healing a lame man. The message is the same: Even though prophet after prophet predicted the life of Jesus, those listeners had still been guilty of taking his life from him--that is, until he rose to take it back. In Acts 13, Paul preaches in the synagogue in Antioch in Pisidia. In all these cases, Jewish history is at the core of the sermon, because it was designed to lead up to One through whom all nations of the earth would be blessed (Genesis 12:1-3). In all these sermons, Jesus is exalted as the Son of God, proven so by many different means. And, in all of these sermons, people's irresponsible, irreverent behavior is pointed out, and they are called in some manner to change.

This outline is interesting in the reasoning behind repentance. The apostles did not just call upon people out of the blue to repent and get things right. They gave them good reason. That reason was the truth of the sacrifice and the resurrection of the Son of God. When people were confronted with the historicity of all that happened--the life, death, burial, and resurrection of Jesus, they were confronted with their own sins, as are we. When confronted with this message, all men must make an answer.

Many make their answer to not repent. Many in the Book of Acts made their answer to reject the teaching. Paul rebuked sharply those who harassed him the next Sabbath in Antioch in Pisidia (Acts 13:44-46). The listeners of Stephen's lone-recorded sermon responded with a barrage of rocks rather than a humble penitence (Acts 7:54ff.) The same kinds of people are still about. There are those who refuse to repent.

And why do they do so? They must not believe. That is not too hard to understand. Modern man observes the same phenomenon. Many are openly antagonistic toward Christianity and Christians because, well, they just don't believe.

What is difficult to grasp is why people would be hypocritical. Why would some pretend to be religious, but not repent? They pretend to believe, they claim allegiance to Christ, but they live in quite different manners. One wonders if, down deep, they really do not believe in the Deity of Christ. Are they using the church for social contact or family appeasement, while secretly holding that those who do believe in Christ are foolish?

If (since) Christ really is the fulfillment of prophecy, he deserves all men's attention. If Christ really resurrected and ascended to heaven (and he is), he deserves all mankind's allegiance. If Christ is who he says he is, he deserves the devotion of all. But some do not give it to him, even while pretending to do so. One can only wonder why that is.

[Many in western society seem unaware of what true conversion is and at what cost it comes respecting Christ as well as so much of this world's ways that really must be jettisoned. Alas, many "converts" need to be truly converted. ~ Editor]