This is the cause why Joshua did circumcise: all the people who came forth out of Egypt, who were males, even all the men of war, died in the wilderness by the way, after they came forth out of Egypt.
"Flint knives [cf. Exodus 4:25] are sharpened by chipping away at the edge of the stone, so that clean, sterile stone is exposed, since bacteria and viruses cannot grow in rock. Circumcision was thus performed with an instrument possessing comparable sterility to today’s surgical scalpels. In view of the likelihood of infection following this operation with a contaminated instrument, use of the flint knife was enormously beneficial and therefore commanded by the Ultimate Healer (or in this case the preventer). [Note: Jay D. Fawver and R. Larry Overstreet, "Moses and Preventive Medicine," Bibliotheca Sacra 147:587 (July-September):277.] 