But your little ones, which ye said should be a prey, them will I bring in, and they shall know the land which ye have despised.
Likewise when the LORD sent you from Kadesh-barnea, saying, Go up and possess the land which I have given you; then ye rebelled against the commandment of the LORD your God, and ye believed him not, nor hearkened to his voice.
And to whom sware he that they should not enter into his rest, but to them that believed not?
So we see that they could not enter in because of unbelief.