The Gospel in Acts

There is a repeated message in the Acts - the apostles preached about the kingdom of God and Jesus.

Acts 1:3
After his suffering, he [Jesus] showed himself to these men and gave many convincing proofs that he was alive. He appeared to them over a period of forty days and spoke about the kingdom of God.

Acts 8:12
But when they believed Philip as he preached the good news of the kingdom of God and the name of Jesus Christ, they were baptized, both men and women.

Acts 14:21-22
They preached the good news in that city and won a large number of disciples. Then they returned to Lystra, Iconium and Antioch, strengthening the disciples and encouraging them to remain true to the faith. "We must go through many hardships to enter the kingdom of God," they said.

Acts 19:8
Paul entered the synagogue and spoke boldly there for three months, arguing persuasively about the kingdom of God.

Acts 20:25
"Now I know that none of you among whom I have gone about preaching the kingdom will ever see me again.

Acts 28:23
They arranged to meet Paul on a certain day, and came in even larger numbers to the place where he was staying. From morning till evening he explained and declared to them the kingdom of God and tried to convince them about Jesus from the Law of Moses and from the Prophets.

Acts 28:31
Boldly and without hindrance he preached the kingdom of God and taught about the Lord Jesus Christ.

Again, the Christadelphians have picked up this emphasis nicely. But what exactly did the apostles say about the kingdom of God in their preaching?