Hebrews 3:17-19

King James Version

¹⁷ But with whom was he grieved forty years? was it not with them that had sinned, whose carcases fell in the wilderness?

¹⁸ And to whom sware he that they should not enter into his rest, but to them that believed not?

¹⁹ So we see that they could not enter in because of unbelief.