'Because of Unbelief' in the Bible

So we see that they could not enter in because of unbelief.

Seeing therefore it remaineth that some must enter therein, and they to whom it was first preached entered not in because of unbelief:

entered not in because of unbelief, He again, after so long a time, fixeth a certain day, saying by David, To-day; as it was said before, To day, if ye will hear his voice, harden not your hearts.