In Exod 4:23, God warns that he will kill Pharaoh’s son because Pharaoh has refused to release God’s son, namely his people (4:22). Why then does the text move directly from this threat to kill Pharaoh’s firstborn (4:23) to the Lord seeking to kill Moses (4:24)? And what does the Lord’s plan to kill Moses have to do with Moses’s own son (4:25)?
Stubborn Moses’s encounter with the Lord here contrasts starkly with the Lord’s benevolent appearance to faithful Abraham in Gen 18. Likewise, Jacob struggled at night with the angel of the Lord and came out with a limp, but he at least persevered until he got a blessing. Moses’s confrontation with God here nearly precipitates his death. This account in Exod 4 is so concise that its meaning seems ambiguous, perhaps clearer to earlier hearers who had heard fuller versions of the story. But the connections between Pharaoh’s son and Moses’s son may suggest a meaning.
Apparently Moses’s offense is not circumcising his firstborn son (4:25); such circumcision would mark Moses’s son as a member of the covenant people that are God’s own son (4:22). God would slay Egypt’s firstborn to redeem God’s own firstborn (4:23), but Moses has not surrendered his own son to God. Moreover, Moses’s resistance is apparently because of his wife’s refusal to allow the circumcision (although she surrenders, she seems quite unhappy about the Lord’s demand in 4:25). (Even in Egypt, Israelites practiced circumcision, as Josh 5:5 testifies; Egyptians also used flint knives when they circumcised, although for them it was not a sign of the covenant. Although Gen 25:2 lists Midian as a child of Moses and Moses presumably circumcised all his children [17:12-13, 26-27], Midianites, or at least Zipporah, did not want to follow the practice.)
If Zipporah has been the one resisting circumcision, why is Moses the one to face punishment? Moses is the Israelite and the one to whom the Lord has spoken, so he is responsible to act on God’s will; the Lord is going to punish him, not his wife, if he refuses to obey. So Zipporah has to sacrifice her son’s foreskin to save Moses’s life. We don’t know the son’s age at this point, but it is not clear that he is merely a baby. He may well have been old enough to voice his own concerns. Of course, even a baby can communicate his displeasure with pain vocally even if he cannot do so verbally.
Zipporah touches the bloody foreskin to Moses’s feet, by this blood from her firstborn apparently atoning for Moses. This act may resemble the way that God later accepted the Passover lamb’s blood in the place of the death of Israel’s firstborn when God struck the firstborn of Egypt. (God later required Israel to redeem every human firstborn with the firstborn of a donkey or a lamb; Exod 13:13; 34:20.) Why she touches Moses’s feet is hard for us to understand at this remove. Perhaps it was because feet were considered one of the dirtier and more disgusting parts of the body; or because they were traveling (though it is not clear that YHWH’s attack on Moses involved this); or as a sign of submission (given the association of the soles of feet with conquest; also cf. 1 Sam 25:41); or an accusation of violence (1 Kgs 2:5); or, perhaps likelier, because of an association with marital duties (cf. Deut 25:9; Ruth 3:4, 7-8) connected with her complaint about him being a “bridegroom involving blood.”
God would defend God’s son by killing Pharaoh’s son. Moses needed to circumcise his own son, identifying fully with God’s covenant, or God could kill him as God could kill Pharaoh’s son. Whatever else this may mean, it offers us a warning. The servant of God with a mission remains responsible to obey God’s covenant at home as well as in public.