Matthew Henry Commentary Exodus 18:1-6

"Now Jethro, the priest of Midian, Moses` father-in-law, heard of all that God had done for Moses, and for Israel his people, how that Jehovah had brought Israel out of Egypt. And Jethro, Moses` father-in-law, took Zipporah, Moses` wife, after he had sent her away, and her two sons; of whom the name of the one was Gershom; for he said, I have been a sojourner in a foreign land: and the name of the other was Eliezer; for [he said], The God of my father was my help, and delivered me from the sword of Pharaoh. And Jethro, Moses` father-in-law, came with his sons and his wife unto Moses into the wilderness where he was encamped, at the mount of God: and he said unto Moses, I, thy father-in-law Jethro, am come unto thee, and thy wife, and her two sons with her." — Exodus 18:1-6 (ASV)

Jethro came to rejoice with Moses in the happiness of Israel, and to bring his wife and children to him. Moses must have his family with him, so that while he ruled the church of God, he might set a good example in family government (1 Timothy 3:5).