God kills Moses?

24 As Moses was on his way to Egypt, he stopped at a resting place for the night. The Lord met him there and tried to kill him.25 But Zipporah took a flint knife and circumcised her son. Taking the skin, she touched Moses' feet with it and said to him, "You are a bridegroom of blood to me."26 She said, "You are a bridegroom of blood," because she had to circumcise her son. So the Lord let Moses alone. Exodus 4:24-26

Why would God try to kill Moses after sending him on a mission to free his people in Egypt? Various commentaries talk about Moses failing to circumcise his son. But since he grew up in Pharohs house, he quite likely did not know about the Abraham covenant. So why would'nt God come and say something to him instead of just coming down to waste him?

Discussion PLEASE.....

From the beginning of chapter four Moses question GOD what if they don't believe. So GOD gave Moses the two signs, the staff and the leprous hand. And Moses still didn't want to take on this mission. So GOD did get angry and said send Aaron. But in chapter seventeen in Genesis, The circumcision was a covenant between me and you and your descendants after you [Abraham]. So when Zipporah cut off the foreskin from her son and touch Moses feet, this was a reminder that you GOD almighty did make a promise with our fathers before.

Zipporah probably knew.