When we look back into the history revealed in Genesis, we understand that when Moses separated himself from Midian to be with his Israelite brothers, he was moving his allegiance from Midian, the fourth son of Abraham (and his wife Keturah, Genesis 25:1; 1 Chronicles 1:32), to Isaac, the firstborn son of Abraham. The years of kinship with Jethro were possible because this priest of Midian was a friend of God
(the meaning of the name Reuel,
Exodus 2:18), but without the benefit of God’s gracious direct revelation, it appears that Jethro and his family had remained separated from the covenant line maintained through Isaac and Jacob, and had not (yet) joined the covenant people of God with the sign of circumcision. In later books of the Bible, we read that, although the Midianites remained hostile (Numbers 22:4–7), the Kenites, who were Jethro’s descendants, followed Moses’ and Jethro’s examples and dwelled among the Israelite tribes in the Promised Land (Judges 1:16; Judges 4:11, Judges 4:17; Judges 5:24; Numbers 10:29–32; 1 Chronicles 2:55; it is noteworthy that the famous Jair, who killed Sisera, was the wife of Heber the Kenite). Perhaps foreshadowing this future entrance into the covenant people of God, Jethro tells Moses to go in peace.
Everybody understood that this was not like moving from one church to another church, but more like moving from one religion to Christianity. Moses’ decision to join the circumcised, covenant people of Yahweh, the God of Abraham, Isaac, and Jacob, would have major consequences for Jethro, his daughter Zipporah, and the children. In order to worship him rightly and to receive the inheritance of the firstborn son, it was necessary for God’s chosen people to remain distinct from those who were still outside the promises and obligations (law) of the covenant relationship.
20 So Moses took his wife and his sons and had them ride on a donkey, and went back to the land of Egypt. And Moses took the staff of God in his hand.