Albert Barnes Commentary Joshua 5:2

"At that time Jehovah said unto Joshua, Make thee knives of flint, and circumcise again the children of Israel the second time." — Joshua 5:2 (ASV)

Make you sharp knives – Translate this instead as in the margin, and compare the marginal reference and note. Knives of flint or stone were in fact used for circumcision and retained for that and other sacred purposes, even after iron had come into common use.

This translation from the margin is adopted by almost all ancient versions, by most commentators, and by the Church Fathers generally. They naturally regarded circumcision performed by Joshua with knives of stone or rock as symbolic of the true circumcision performed by Christ, who is more than once spoken of as the Rock (compare to 1 Corinthians 10:4; Romans 2:29; Colossians 2:11). See Joshua 21:42.

Circumcise again ... – That is, make a people who were once circumcised, but are not so now, a circumcised people once more. .