Parallel
Hebrews 3:19
Nestle 1904 Greek New Testament · 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.