Include verse 23. My comments in black. Exodus 4:23-26 (KJV)
[SUP]23 [/SUP] And I say unto thee, Let my son go, that he may serve me: and if thou refuse to let him go, behold, I will slay thy son, even thy firstborn.
That was what Moses was told to say to the king of Egypt, commanding him to release God's "son" Israel that they could serve God. That had a dual application. God wouldn't allow Moses to go do that, jeopardizing Israel's release, because Moses was disobeying the Abrahamic Covenant requiring all males to be circumcised. The Hebrews would have rejected Moses as deliverer since he was allowing an unclean son to live. So how could Pharaoh be told his own first born son would die if he refused?
[SUP]24 [/SUP] And it came to pass by the way in the inn, that the LORD met him, and sought to kill him.
There's nothing after verse 23 to indicate God decided to kill Moses the intended messenger. For whatever reason Moses had neglected to circumcise the boy, and since the boy was allowed to live, God intended to kill the boy. Even with Moses there with Zipporah and son facing off with God at the inn (water hole), Moses just wouldn't cut the boy. Zipporah realized she was about to lose her precious son, so usurped authority, a woman circumcising her son. Men circumcise males. Sarah, Abraham's wife, was never told to do that. Neither was it proper for Zipporah, but she did it, turning God back from killing the boy. A mother would , I suspect, find doing such a bloody thing to a baby would be difficult. She saved that life, and cleared the way for Moses to continue on mission, to be met by Aaron coming up from Egypt by the guidance of God.
[SUP]25 [/SUP] 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.
[SUP]26 [/SUP] So he let him go: then she said, A bloody husband thou art, because of the circumcision.
Moses could have stopped her, but stood by allowing. That was an act of releasing the boy to be right before God in that part of the covenant, released to serve God, which he would not be allowed to do if not circumcised. In the same manner Pharaoh would have to release Israel by obeying God or lose his son.
It isn't said why Moses halted at that law, perhaps so highly favoring the baby of his advanced age he just couldn't do anything bloody to him, but we know from previous verses he was extremely reluctant to accept God's plan to be sent on that mission. Moses was subject to the wrath of God for that too, just before this event. It's amazing he didn't get his act in order then too.
Zipporah the heroine! She had good reason to chasten her husband.
How many daddys today are neglecting their sons and daughters by not seeing to them being free to serve the Lord? We ought not make pets or mostly friends out of our children, but do all we know to do to prepare them, whatever it takes within the law.