Also not exclusive. Some hear the truth and believe, some hear the truth and reject it (they have "not believed"). There is a possible third category of those who have not heard and do not "believe or disbelieve". Like it or not, David fell into that category. He certainly WOULD HAVE believed in Jesus (and I'm sure right after the crucifiction he got his chance). But he didn't at the time.
You have also opened WIDE the door of what constitutes "belief in Jesus" since men who had never heard the name get full credit.They believed the PROMISE ( Hebrews)
The OT saints were saved by faith , just as the NT saints..they looked forward to the promise as we look back
Their faith was a gift also .
."All that are Israel are not Israel"
They believed the PROMISE Yes. And Jesus saying I am the way.... No man comes unto the Father but by Me" did not invalidate that promise.
Their faith was a gift also.
We weren't debating Calvinism... Yes, their faith was a gift, otherwise they would ahve reason for boasting.