This is surely one of the strangest, enigmatic passages in the entire Old Testament:
“And the LORD said to Moses, “When you go back to Egypt, see that you do before Pharaoh all the miracles that I have put in your power. But I will harden his heart, so that he will not let the people go. Then you shall say to Pharaoh, ‘Thus says the LORD, Israel is my firstborn son, and I say to you, “Let my son go that he may serve me.” If you refuse to let him go, behold, I will kill your firstborn son.’”
At a lodging place on the way the LORD met him and sought to put him to death. Then Zipporah took a flint and cut off her son’s foreskin and touched his feet with it and said, “Surely you are a bridegroom of blood to me!” So he let him alone. It was then that she said, “A bridegroom of blood,” because of the circumcision.” (Exodus 4:21-26)
What in the world is this final scene supposed to mean, in which (apparently) God seeks to kill Moses’ son for not being circumcised? This thwarted divine attempt not only seems overly harsh, but to most modern readers it comes out out of nowhere and violates the narrative flow of the surrounding context. What should we make of this?
Stephen Dempster, in my favorite Old Testament book Dominion and Dynasty: A Theology of the Hebrew Bible, provides several important clues. He first points out that Moses often represents Israel as a whole in the book of Exodus, experiencing in his own life what the nation will later collectively experience:
“The figure of Moses, this child born as a type of savior figure, not only saves Israel but also embodies Israel at times. His rescue from the water prefigures the nation’s salvation from the water; his escape after the death of an Egyptian (Exod. 2:11-15) is a prelude to the Israelites’ flight after the death of many Egyptians (Exod. 12:29-39); his experience of being in the desert for forty years (Exod. 2:21-25) foreshadows the same for Israel (Num. 14:33); his divine encounterbefore the burning bush (Exod. 3) anticipates Israel before the fire at Sinai (Exod. 19-24).” (p. 94)
Now let’s take another look at the mystery of Exodus 4:21-26. The first observation to make is that there is a clear parallel between 4:21-23 and 4:24-26. In the earlier section, God reveals to Moses what the future holds as he journeys back to Egypt. Because Pharaoah will not release Israel–God’s own “firsborn son”–from slavery, God will “kill” Pharoah’s own “firstborn son.” Thus here we have a clear foreshadowing of the judgment that will soon come on Egypt (the plagues) and the redemption which Israel will experience as a result (the Exodus). Looking now at Exodus 4:24-26, notice how the same pattern of “God” seeking to “kill” a “firstborn son” reappears–only this time, it is Moses’ firstborn son who is threatened with death. However, Moses’ firsborn son is finally spared in contrast to the death of Pharaoh’s firsborn son. Why?
The answer is found in the strange telling of an abrupt, emergency circumcision. Not only are we told that Moses’ wife (Zipporah) circumcised their son, but further that she “touches” his feet with the dead, bloody foreskin she has cut off [note: the ESV's decision to render "his feet" in Hebrew with "Moses' feet" is surely wrong]. This act then causes the Lord to abstain from killing the firsborn son of the one who embodies Israel immediately after a prediction that God will kill Pharaoh’s son.
Sound familiar? The order of events that are foreshadowed in Exodus 4:21-26 proceed exactly as they appear later in the story. First, God judges Egypt with the ten plagues, and Pharaoh’s firstborn son is killed. Then, Israel (God’s firsborn son) is delivered when they “touch” (Exodus 12:22) the blood of the dead lambs upon their doorposts, causing the judgment of God to “pass over” them in sparing mercy–which is exactly what happens with Moses’ son here. In both Exodus 4 and the later Passover, there is a violent act of cutting that draws blood, and being “touched” with the blood leads to salvation from the wrath that is poured out on the enemy of God’s people. As Dempster notes, Exodus 4:24-26 is a “proleptic Passover” (p. 98).
Conclusion: just as Exodus 4:21-23 foreshadows the ten plagues of judgment upon Egypt, so 4:24-26 foreshadows the Passover ritual which will cause God to spare His firsborn son, Israel.