Why was the Lord about to kill Moses in Exodus 4?
Exodus 4:24-26, along with Genesis 6:1-4, ranks as one of the most difficult and enigmatic passages in the Old Testament. Aspiring exegetes, thrilled to exercise the whole repertoire of interpretive principles ranging from textual criticism to word study, see this passage as a gold mine. The rest of us tend to avoid it like a land mine!
Although the grammar is straightforward, the use of pronouns without clear antecedents creates numerous ambiguities. In addition, the brevity of the passage gives very little context for interpreting the vocabulary. Consequently, the narrative raises many exegetical questions without obvious answers, ranging from whom Jehovah attacked to the meaning of the expression “bridegroom of blood.”
The traditional view held historically by Christian exegetes (and the position advocated here) is that God attacked Moses because he neglected to circumcise his son. The pericope insinuates marital tension in the household. Moses, a Jew, and that, too, a Levite, surely would have wanted his son circumcised but yielded to Zipporah’s resistance and desire. As a Gentile, she probably found this practice repulsive, which could explain her violent outburst against Moses when she “threw the foreskin at his feet” (4:25). Moses, as head of his home, was remiss in not carrying out this divinely commanded mark of separation. Judgment begins with God’s household. How could Moses rule God’s household if he could not “rule his house well”? God threatened Moses with death to awaken both their consciences to this sin. God certainly could have killed Moses as the law demanded but stayed His hand to force Zipporah’s in enacting the rite. By her act, he became a “bridegroom of blood because she was compelled to acquire and purchase him anew by shedding his blood.”
This short narrative teaches us that there are no trifling commandments in Scripture; God takes all of them seriously and expects His people to do so. “Great principles are involved in very insignificant acts as ponderous bridges revolve on small pivots … we may be conscious of having been sent for some great work for God and yet shrinking from some small duty (circumcision) … our action in common places of life (home life) is deciding our destiny …. He chastens whom He loves …. Be careful to ascertain the evil thing that grieves Him and put it away.”
 The Septuagint says Zipporah “fell at His feet” and not that the foreskin “touched his feet” (Note the italics). The Rabbinic interpretation indicates that Zipporah laid the foreskin at the feet of the “Angel of the Lord,” that the pericope emphasizes circumcision and sees Moses’ son as the one who was attacked.
 The Septuagint translates “bridegroom of blood” as “blood of circumcision.” For the interesting etymological link between “hotan” (circumcision) and “hatan” (“bridegroom” or “father-in-law”), see Ernst Kutsch, “hatan,” in Theological Dictionary of the Old Testament, ed. G. Johannes Botterweck and Helmer Ringgren (Grand Rapids, MI: William B. Eerdmans Publishing Company, 1986), 5:271.
 Keil & Delitzsch. Commentary of the Old Testament Vol 1.
 F.B. Meyer, Moses. Italics are mine.