Q. If the fullness of the Gentiles being saved must arrive before the rapture occurs, what about all the people that are continually being born that need to be saved, how could the gentile number ever be final?
A. Paul borrowed the phrase “full number” in Romans 11:25 from nautical terminology. It didn’t mean the full number of sailors in the general sense, just the pre-determined number required to man a particular ship. Just so, the full number of Gentiles is simply the pre-determined number required to complete the Church.
There were believers before the Church and there will be believers after the Church, but there is apparently a specific number pre-determined to be in the Church. When that number is reached the Church will disappear.