“Be it known therefore to you, that this salvation of God is sent to the Gentiles. They will also hear.”
Meanwhile let them know, (and he wanted to provoke them to jealousy by this - Romans 11:11) that this salvation of God available through the Messiah is sent to the Gentiles who will hear it, just as many Jews do. True ‘Judaism' is now open to the world.
‘They also.' Also as well as the believing Jews. So it was now open to all Jews to consider their response, recognising that some Jews had already responded and that many Gentiles were also to receive God's offer and would hear. He did not want them to be left behind. And on that note they departed, with some believing, some considering, and some saying, ‘No way!'.
The thing that stands out most strongly from these last few verses, and the lack of any reference to the church separately in this final passage is that Paul is still concerned that Christianity be seen and recognised as the true fulfilment of Judaism. To him the church is the Israel of God. It is not a question of choosing between being a Jew or a Christian, it is a matter of a Jewish Christian being the true Jew, and the Christ-rejecter not being a true Jew. Those who believe are engrafted. Those who do not believe are cut off (Romans 11:17-27). And while Gentile Christians may not practise all the customs of the Jews, they do become an essential part of Israel (Romans 11:17-27; Galatians 3:7; Galatians 3:28; Galatians 6:16; Ephesians 2:11-22; James 1:1; 1 Peter 1:1; Revelation 7:4-8). For as will be later pointed out they are circumcised with the circumcision of Christ (Colossians 2:11). Their offerings are offered once for all through the sacrifice of Himself offered by their great High Priest (Hebrews 7-10). Thus the growth of the Kingly Rule of God is the growth of the true Israel as laid on the foundation of the Jewish Christian Apostles. Salvation is of the Jews (John 4:22; Isaiah 2:2-4)).
The Conclusion.
This general statement brings to a conclusion and stresses all that Acts has been aiming for, the proclamation of the Kingly Rule of God, and of the risen Lord Who is responsible for that Kingly Rule, both in heaven and in earth. And it brings out that God has made it possible for this to occur in peace and safety, at the very heart of the Empire itself.