That’s a good question, what do we know?
I think the NT represents a major update of the OT, in knowing God and knowing our ideal relationship with God.
We know much more in the NT that we can’t save ourselves as the OT seems to suggest. We need the ultimate Anointed One. We know a lot more about faith, which is hardly discussed explicitly in the OT (correct me if I’m wrong on that one).
We know that faith does matter, so do faithfulness and suffering.
We know what is important. We know the Way, the Truth, and the Life.