v 20 I asked you to come here today so we could get acquainted and so I could explain to you that I am bound with this chain because I believe that the hope of Israel—the Messiah—has already come.
Wherever Paul went he made it his habit to meet up with the Jews in that area. He had earlier written to these believers in Rome ‘Dear brothers and sisters, the longing of my heart and my prayer to God is for the people of Israel to be saved. I know what enthusiasm they have for God, but it is misdirected zeal.’ (Romans 10) The Jews were people who shared his culture, and were already familiar with the stories and relationships of the Old Testament. He felt an obligation to go first to the people he knew best.
In that sense Mission usually begins at home – with the culture and background we know best. I suspect that young people will not become missionaries by going to a distant culture until there is some concept of what reaching out to their own culture means in practice.
So Paul gets the local Jews together and sets out to announce that the Messiah – for whom they all looked – had now appeared. There was however some prejudice (v 22) ‘we want to hear what you believe, for the only thing we know about this movement is that it is denounced everywhere.’ That is all Paul needs to seize the opportunity of speaking about Jesus.