John 17:6
I know this sounds like Yoda talking, but the fact that Jesus says “yours they were” shows that God didn’t CHANGE from the OT to the NT.
People belonged to God and were faithful to Him and experienced some sort of grace before Jesus came. It wasn’t the fullness of salvation that Jesus would finally bring about, but God wasn’t some angry, closed off deity like your Sunday school classes may lead you to believe. He’s been in the saving & redeeming & keeping business a long long time.