Exodus 4:25

Zipporah took a sharp stone. Egyptian surgeons commonly used stone knives. According to Joshua 5:2 these were also the usual instruments for performing the rite of circumcision.

Cut off the foreskin. Moses returned to Egypt with his two sons (see Exodus 4:20). Evidently Gershom, the elder, had been circumcised in accordance with God’s instructions to Abraham (Genesis 17:10-14). In the case of Eliezer, the younger son, this rite had been neglected (Patriarchs and Prophets, p. 256). Not believing in the necessity of circumcision, Zipporah had resisted her husband’s intention to circumcise Eliezer at the appointed time. The appearance of the angel made it clear that her opposition did not excuse Moses from administering the rite. Now that her husband’s life was in danger she found it necessary to carry out the operation herself.

A bloody husband. These words are clearly an expression of reproach. They show that Zipporah performed the rite grudgingly, not from a desire to obey God, but of necessity, to save her husband’s life. Her meaning seems to be that Moses was a poor sort of husband, on whose behalf it was necessary to shed the blood of her sons in compliance with a national custom she regarded as barbarous.