Treasury of Scripture Knowledge
I will therefore put you in remembrance, though ye once knew this, how that the Lord, having saved the people out of the land of Egypt, afterward destroyed them that believed not.
1 Corinthians 10:1
For I do not want you to be unaware, brethren, that our fathers were all under the cloud and all passed through the sea;
Who were they who heard and rebelled? Were they not all those Moses led out of Egypt?
Therefore, while the promise of entering his rest remains, let us fear lest any one of you be judged to have come short of it.
Five of them were foolish, and five were wise.
1 Corinthians 10:5
Nevertheless, with most of them God was not pleased; for they were overthrown in the wilderness.
1 Timothy 5:15
For some have already turned aside to follow Satan.
So we see that they were not able to enter because of unbelief.