Jamieson, Fausset and Brown on Joshua 5:4-7

4-7. this is the cause why Joshua did circumcise--The omission to circumcise the children born in the wilderness might have been owing to the incessant movements of the people; but it is most generally thought that the true cause was a temporary suspension of the covenant with the unbelieving race who, being rejected of the Lord, were doomed to perish in the wilderness, and whose children had to bear the iniquity of their fathers (Nu 14:33), though, as the latter were to be brought into the promised land, the covenant would be renewed with them.