When the condition for the rapture to begin is met- the full number of Gentiles have come in. What about the Jews that are saved in this Church age? Why are they not mentioned, too? Isn’t there a full number of them, too?
When Paul spoke these words in Romans 11:25 the Church was primarily made up of Jewish believers, and their number was steadily growing. He had recently been to the Council at Jerusalem where he heard James say that the Lord was going to take a people for Himself from among the Gentiles (Acts 15:13-14).
I think everyone there believed that meant the door would be opened for Gentiles to come into the Church in addition to the Jewish people who were also coming. In Romans 11:25, Paul hinted that the number of Gentiles was known to the Lord and the fulfillment of this number would trigger the rapture as well as the lifting of the partial hardening that had come upon Israel due to their rejection of the Messiah.
Also, it’s important to distinguish between Israel as a nation and individual Jewish believers in Jesus. The leaders in Jerusalem knew Israel’s days were numbered because the Lord had told them so (Matt. 24:2, Luke 19:41-44) . The issue was not how many Jewish believers there would be. It was whether Israel would be restored as a nation. James assured them that after the Lord had gathered the Gentiles, He would turn again to Israel (Acts 15:16-18) and restore the nation to its covenant relationship with God. Based on Ezekiel 39:22, I believe this will happen with the Battle of Ezekiel 38.
No one knows how many Jewish people have become believers in Jesus in the meantime, but there’s no mention of a predetermined number of Jews who would come into the Church as there is with the Gentiles.