Exodus 4:24 says: "And it came to pass on the way, at the encampment, that the Lord met him and sought to kill him."
Whether it was Moses or his son whom God sought to kill has been disputed by a number of Hebrew scholars. Verse 24 does not clearly give the answer. But it is clear from the story that Moses was the one at fault. Moses knew that all Israelites were to be circumcised when they were eight days old. However, his wife was not an Israelite and did not believe in circumcision. It appears that Moses let his wife have her way; and in doing so, he failed to obey God's command to circumcise his son (Genesis 17:10-14).
If you will read all of Exodus 4, you will see that Moses was going back to lead God's people, Israel, out of Egypt. God could not allow His direct representative to lead the entire nation of Israel if he wasn't obedient in all things and if he wasn't leading his household as he should have.
For an additional study tool, please read our booklet You Can Have Living Faith.