It may be as simple "why the Lord sought to kill him" as reading what happened next.
24 And it came to pass by the way in the inn, that the Lord met him, and sought to kill him. 25 Then Zipporah took a sharp stone, and cut off the foreskin of her son, and cast it at his feet, and said, Surely a bloody husband art thou to me. 26 So he let him go: then she said, A bloody husband thou art, because of the circumcision.
This is an interesting translation that comes from the Greek translation of the Old Testament--the Septuagint--made by Jewish scholars close to the time of Christ.
Exo 4:25 AndG2532 Zipporah, takingG2983 G* a small sharp stone,G5586 circumcisedG4059 theG3588 foreskinG203 G3588 of her son.G5207 G1473 AndG2532 she fellG4363 atG4314 G3588 his feet,G4228 G1473 andG2532 said,G2036 [6is stoppedG2476 1TheG3588 2bloodG129 3of theG3588 4circumcisionG4061 G3588 5of my male child].G3813 G1473
Regardless, the effect of the Lord seeking to kill Moses was for Zipporah to circumcise Moses' and her son. (Wisdom is justified of her children).
All this was during the time that the Lord was instructing Moses (in the simplest terms) on how to tell Pharaoh about the death of his first son, the entire episode seems to me to be a physical foreshadowing of that event by the circumcision of his own son. Circumcision is a symbol of "putting to death".
That's about as far as I'm willing and able to go--right or wrong.