I have a question about post-church salvation. I think I agree with your view about OSAS being only for the church, I wonder how it would be possible for tribulation believers to maintain their own salvation. Isn’t it impossible in any context? Will the Holy Spirit be helping them keep up their strength?
Old Testament believers were able to do this and post Church believers will be in the same situation as they were. It requires a much greater behavioral awareness than you and I are used to, but the consequences of failure will also be much clearer. Having observed Orthodox Jews in Israel, I saw how carefully they guard their behavior and how they develop an almost intuitive reaction to anything that might tempt them to sin.
The Holy Spirit will be with post Church believers as He was with Old Testament believers, the difference is He won’t be sealed within them.
Jesus explained this distinction to His disciples in John 14:16-17. Before the crucifixion the Holy Spirit was with them, but afterward He would be in them. This is a blessing unique to the Church.