There seems somewhat obscure in this verse. Probably, as Zipporah was of Midian, she had prevailed upon Moses to neglect the rite of circumcision. And if so, this omission was highly sinful. See Genesis 17:14. The sins of God's people are cutting things, and will not pass unvisited. Psalms 89:30-32.
Related Commentaries of Exodus 4:24
Exodus 4:24
24 And it came to pass by the way in the inn, that the LORD met him, and sought to kill him.