Joshua 5:4-6

Joshua had to circumcise all the men and boys—all the fighting men. Although they had been circumcised before leaving Egypt, the male children born during the forty years they spent in the wilderness had not been circumcised. Also, by the end of that forty years, all the fighting men who had come out of Egypt had died because they had not listened to the voice of YAHWEH. So YAHWEH had made an oath that they would not see the land he had promised to give their ancestors, a fertile land.