John Gill Commentary Joshua 5:6

"For the children of Israel walked forty years in the wilderness, till all the nation, even the men of war that came forth out of Egypt, were consumed, because they hearkened not unto the voice of Jehovah: unto whom Jehovah sware that he would not let them see the land which Jehovah sware unto their fathers that he would give us, a land flowing with milk and honey." — Joshua 5:6 (ASV)

For the children of Israel walked forty years in the
wilderness
Wanting a few days, the round number is given: not forty two, as the Septuagint version:

till all the people [that were] men of war, which came out of Egypt ,
were consumed ;
all that were above twenty years of age, excepting Joshua and Caleb:

because they obeyed not the voice of the Lord ;
but murmured against him, and against his servants, and particularly against Aaron, being the high priest; and chiefly because of the report of the spies, and their murmurs then, which so incensed the Lord against them, that he threatened them with an entire consumption of their carcasses, and which accordingly was fulfilled, to which the following clause refers:

unto whom the Lord sware, that he would not show them the land which
the Lord sware unto their fathers that he would give us, a land that
floweth with milk and honey ;
see (Numbers 14:23Numbers 14:24) .