Judges 6:16 (AMP)
The Lord answered him, “I will certainly be with you, and you will strike down the Midianites as [if they were only] one man.”
Judges 6:16 (RSV)
And the Lord said to him, “But I will be with you, and you shall smite the Mid′ianites as one man.”
Hebrews 3:19
So we see that they could not enter in because of unbelief.