You’ve written that the old testament saints were saved if they died believing that God would fulfill His promise to send the Redeemer (Genesis 12:3). Although they never saw Him, their faith saved them. Perfect, I got it. But you’ve oft times also written that the Holy Spirit deals differently with the church than any other group of people. I believe that too. Therefore OT saints (like post-rapture believers will) had to remain faithful in order to keep their salvation because they are not sealed with the Holy Spirit like church age people are. But doesn’t this imply a works-based salvation rather than a faith-based one? If their faith in the coming Messiah saved them, they shouldn’t have to “work” to keep that salvation.
Old Testament Judaism is a faith plus works religion. They were required to obey the Law as evidence of their faith (Exodus 19:5-6), and could lose their salvation for disobedience. David testified to this when he asked the Lord not to take the Holy Spirit from him after his sin with Bathsheba (Psalm 51:11). Only the church is promised salvation by faith alone (Ephes. 2:8-9), and only the Church is sealed with the Holy Spirit guaranteeing our inheritance (Ephes. 1:13-14).