Exodus 4:25
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. 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.
On the way to Egypt the angel of the Lord met Moses and took a threatening posture as though to slay him. The cause was neglect of God's positive covenant command to circumcise his youngest son, which Moses had left undone after yielding to his wife's refusal and entreaties to postpone the rite from affection for the son. No explanation was given by the angel, and the journey itself was in obedience to God's express command, yet Moses knew at once that the threat to his life was for that disobedience. It was Zipporah herself who performed the circumcision on her youngest son. Fearful that her husband would be slain, she overcame her strong affection and feelings for her son to do what was required.
After the act the angel let Moses go, ending the danger and leaving him free to continue his journey to stand before Pharaoh. Living in neglect of a known divine requirement had left even Israel's chosen leader without the security of angelic protection until he obeyed, since angels could not protect him while he remained in neglect. The neglect reached beyond Moses himself, for it weakened the force of God's precepts among the people. It also left him unfit to go before Pharaoh, where his life would be exposed to the will of the king and would need the presence of God's angels.
The incident points to the time of trouble before Christ's coming, when angels will preserve the righteous but will not protect those who disregard a divine precept.