A.T. Robertson Commentary Hebrews 10:30

"For we know him that said, Vengeance belongeth unto me, I will recompense. And again, The Lord shall judge his people." — Hebrews 10:30 (ASV)

We know him that said (οιδαμεν τον ειποντα). God lives and is true to his word. He quotes De 32:35 (cf. Romans 12:19). For εκδικησις see Lu 18:7f. God is the God of justice. He is patient, but he will punish.

And again (κα παλιν). Deuteronomy 32:36.