The “Kingdom” for Paul and the apostles is an important part of their teaching ministry. In Acts they inquired it and preached it to both Jews and Gentiles alike:
Jesus taught them about it after his resurrection, Acts 1:3.
They asked Jesus about it before he was taken up, Acts 1:6.
They kept preaching about even after he left, Acts 8:12.
They strengthened each other in the hopes of entering it, Acts 14:22.
They evangelized the Jews with it, Acts 19:8.
When they said good bye they hope to see one another in it, Acts 20:25.
Upon reaching Rome Paul preached it there, Acts 28:23.
And he preached with boldness until his death, Acts 28:31.
My questions are: What do you know about the coming Kingdom? And, if it was that important as a future hope to the apostles, why is it now relegated to something that is invisible and already attained in this life and age?