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Hebrews 3:19
Robinson-Pierpont Byzantine Textform · Berean Standard Bible
Καὶ βλέπομεν ὅτι οὐκ ἠδυνήθησαν εἰσελθεῖν δι’ ἀπιστίαν.
So we see that it was because of their unbelief that they were unable to enter.