The account in Exodus 4.24-26 has confounded exegetes for centuries, but it appears to be a late insertion into the text (based on a historical account) that may have derived from Jewish questions regarding how God could use Moses when, having lived as an Egyptian, it is likely that Moses would not have known to circumcise his son in obedience to the command given to Abraham in Genesis 17.10-12.
The story explains for the Jewish reader that God broached Moses with this issue upon his return to Egypt. Perhaps in some lengthy discussion between Moses and God about it (similar to the drawn out discussion between God and Abraham mentioned at Genesis 18.16-33), Moses’ wife Zipporah took it upon herself to circumcise their son (of note, the only woman in Scripture ever recorded as performing a circumcision).
While Moses’ life is spared from what was obviously a heated argument turned deadly, the issue is due not to circumcision but because Moses was being disobedient. (Perhaps this was part of Moses’ ongoing desire for God to use someone else instead of him, similar to Jonah’s protest over being used.) God may have told Moses to circumcise his son and an already reluctant Moses asks, “But why?” And like Jonah, Moses’ frustration and refusal must have escalated into this short account which only mentions the outcome.—Compare Exodus 4.10-14 with Jonah 4.1-9.
The resolution is one understood from a Jewish cultural perspective in which it is “normal” to “argue” points with God (a view still culturally shared among Jews today). Scripture is filled with such incidents, not only Abraham’s discussion regarding Sodom and Gomorrah, but Jacob’s wrestling with an angel (Genesis 32.25-31), Job demanding that God answer for his unjust suffering (Job 7.11; 21.4; 40.1-8; 42.1-6), and Gideon’s testing of the fleece (Judges 6.36-40). The incident in Exodus 4 is possibly one of these situations, but interestingly Zipporah, characteristic of a faithful woman, grows tired of the debate and does what needs to get done, settling the issue.
The expressions that God was trying to kill Moses and the account stating that Zipporah saved the day are not originally meant to be read with Christological overtones, as if claiming that salvation can be attained by another (although that is what is happening with Christ who saves us by His actions). Instead the account gives an explanation on how God must have settled issues about circumcision between Moses and his family before Moses’ assignment, and how a woman, Zipporah, helped move things along.