So much takes place in the first sidrah of the book of Exodus, so many events over so many decades squeezed into so few chapters, that it is all too easy to miss Exodus 4.24, describing something that occurred just before Moses returned to Egypt to lead his people from slavery to freedom. Having been given his instructions by God, having been told the dreadful end to which the process would lead for the Egyptians, Moses and his family depart from Midian for Egypt.
At their first night encampment, God meets Moses and tries to kill him, and is only dissuaded from following through by Zipporah, Moses's wife, performing a hasty circumcision on one of her sons and assuaging the divine anger with the blood of the deed.
It is a verse when you have to ask yourself, "Did I really hear or read that?" but the verse is in the text and, aberrant though it looks to us, it had to be explained.
In Shemot Rabbah (5:8), the Midrash explains that Moses was to be punished for not circumcising his second son Eleazar, a mitzvah which he had not been able to perform at the correct time. The Targum Pseudo-Jonathan goes further, explaining that Moses had agreed with Jethro, his father-in-law, that one son would not be circumcised out of respect for its grandfather's idolatry; the importance of circumcision being what it was, God would not delay Moses's punishment even for one hour and had Zipporah not acted quickly, Moses would have died and who knows what might have happened then.
This difficult verse is one of many in the Torah that may surprise, puzzle or shock us, but for which there are nearly always explanations somewhere providing you search hard enough. How convincing they are, or whether they deepen rather than clarify the problem, is another matter altogether.