Paul focused on the main issue in his trial: the hope of the resurrection (the belief that the dead will be raised to life). His preaching came from this hope and from the fact that Jesus had risen from the dead.
However, his message was not accepted by either group of Jews because of what it meant. The Pharisees believed in the resurrection, but they could not accept that Gentiles could be included among God’s people without circumcision and without keeping the law of Moses (see 15:5). Yet this is exactly what the resurrection of Jesus and the gift of the Holy Spirit had made possible (see Acts 2:39; 10:34–48).
The Sadducees, on the other hand, did not believe in the resurrection at all. Because of this, they strongly opposed any teaching about the resurrection (see 4:1–2).