RABBI JOSEPH KRESEFSKY answers ...
While the Bible does not precisely state all of G_d's reasons and motives for wanting to kill Moshe, we can take what information is available and derive possible explanations. Although it may seem outwardly there was nothing wrong, to G_d nothing is hidden! The issue surrounds the circumcision of one of Moshe’ sons - it was not done at the proper time, on the eighth day after birth, as G_d commanded.
Exodus 4:24-26 - "And it came to pass by the way in the inn, that the L-rd met him, and sought to kill him. 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. So he let him go: then she said, A bloody husband [thou art], because of the circumcision."
Because only one of Moshe' sons is mentioned here – not having been circumcised, we must assume the other was! This could have been the cause – could it be that Moshe did circumcise his firstborn according to the command of G_d, and Zipporah (not being an Israelite) – was appalled at the bloody act? And in-turn gave Moshe such a hard time over it that he didn't want to go through it again? Possibly, although it could also be a possibility that it goes back to the Covenant that Abba made with His friend Avraham...
Remember from the covenant that G_d made with Avraham, that circumcision was to be a sign of the covenant – because Moshe has neglected to fulfill this part of the Avrahamic covenant, the results of that could have been death to the breaching party, i.e. Moshe.
Genesis 17:9-14 - G_d said to Avraham, "As for you, you are to keep my covenant, you and your descendants after you, generation after generation. Here is my covenant, which you are to keep, between me and you, along with your descendants after you: every male among you is to be circumcised. You are to be circumcised in the flesh of your foreskin; this will be the sign of the covenant between me and you. Generation after generation, every male among you who is eight days old is to be circumcised, including slaves born within your household and those bought from a foreigner not descended from you. The slave born in your house and the person bought with your money must be circumcised; thus my covenant will be in your flesh as an everlasting covenant. Any uncircumcised male who will not let himself be circumcised in the flesh of his foreskin -that person will be cut off from his people, because he has broken my covenant."
G_d knew about the situation and was long suffering in waiting on Moshe to repent. Moshe may have hoped G_d would shut His eyes to the situation and not even bring the matter up.
However, not only was Moshe head of his household, but G_d had picked him to be head of the whole nation of Israel – what kind of example would this have been. Moshe was now going to make a decision – circumcise the boy – or die!
SANDRA JEFFERY answers ...
When God told Moses of what was to come down in the slaying of the Pharaoh’s son and all first born males of every household should the Pharaoh refuse to let the Hebrews out of Egypt, Moses seemed to forget that he never had his first born son circumcised as was required by God’s people.
Zipporah, Moses wife, was of the Hebrew lineage of Abraham, and knew the law of circumcision for God’s Hebrew males (Exodus 2: 21, 22). She herself circumcised their son Gershom, in great anger because of Moses failure in carrying out this requirement (Exodus 4: 25, 26). This was why God was wroth with Moses and sought to kill him – Zipporah, understanding the cause of God’s anger, circumcised their son. If she hadn’t, when the angel of death passed through, Gershom would have died because of Moses disobedience, rendering Moses a murderer by neglect.
RABBI GUTMANN answers ...
This is a very similar issue question to the previous one. "God sought to kill Moses" or did He? The incident certainly produced a response from the hitherto uncooperative Midianite daughter of Jethro, Zipporah! Like it or not she had married into God's covenant people and circumcision! Who said Jewish identity only or even primarily comes through maternal descent? Forget Ephraim and Manasseh if so!
Is this from Rabbinical Halachic law or God's Law? As with the previous question, the answer surely lies in another question, "Who has known the mind of the Lord?" (Romans 11:34 - check out the context and compare also with 1 Cor 2:16).