Jesus after his resurrection continued to teach the disciples concerning the kingdom of God. In the first chapter of Acts we read “After his suffering, he presented himself to them 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. On one occasion, while he was eating with them, he gave them this command: ‘Do not leave Jerusalem, but wait for the gift my Father promised, which you have heard me speak about. For John baptized with water, but in a few days you will be baptized with the Holy Spirit.’ Then they gathered around him and asked him, ‘Lord, are you at this time going to restore the kingdom to Israel?’” (Acts 1:3-6, NIV).
The disciples were at this time still looking for a political restoration of the kingdom of Israel. Jesus told them the time of that was not for them to know. Instead, he told them “But you will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth.” (Acts 1:8, NIV). Paul, in writing to the Corinthians made the connection between the power given by the Holy Spirit and the kingdom of God. “For the kingdom of God is not a matter of talk but of power” (1 Corinthians 4:20, NIV). In his letter to the Roman Christians he wrote “For the kingdom of God is not a matter of eating and drinking, but of righteousness, peace and joy in the Holy Spirit” (Romans 14:17, NIV). This means the kingdom of God is not a matter of religious practices but is lived in righteousness, peace and joy through the presence of the Holy Spirit in the believer.
As for the kingdom of God being proclaimed all over the world, Jesus had already told his disciples, “And this gospel of the kingdom will be preached in the whole world as a testimony to all nations, and then the end will come” (Matthew 24:14, NIV). Jesus also told his disciples, “I must proclaim the good news of the kingdom of God to the other towns also, because that is why I was sent” (Luke 4:43, NIV).
Paul also had a need to proclaim the good news of the kingdom. We are told in Acts 19:8 (NIV) “Paul entered the synagogue and spoke boldly there for three months, arguing persuasively about the kingdom of God.” Later in Acts we read “They [the Romans] arranged to meet Paul on a certain day, and came in even larger numbers to the place where he was staying. He witnessed to them from morning till evening, explaining about the kingdom of God, and from the Law of Moses and from the Prophets he tried to persuade them about Jesus” (Acts 28:23, NIV). During two years in Rome Paul welcomed visitors to his rented house and there “He proclaimed the kingdom of God and taught about the Lord Jesus Christ—with all boldness and without hindrance! (Acts 28:31, NIV). It is hard not to see that the kingdom of God had a large place in Paul’s proclamation of the gospel.