New Defender's Study Bible Notes
18:1 Jethro. See note on Exodus 3:1. Indications are that Jethro knew and worshipped the true God; the Midianites were descendants of Abraham, through Keturah, and since Jethro (or Reuel) was a priest of Midian, it seems that at this time in their history the Midianites had not yet descended into paganism. Note Exodus 18:11,12.
18:11 they dealt proudly. This is the first mention in the Bible of the sin of pride, and it is significant that it is referring to the primeval sin of “the gods”–that is, the supposed deities of the pagan nations. The first sin was that of Lucifer, or Satan, who aspired to dethrone God (Isaiah 14:12-15; I Timothy 3:6).
18:16 statutes of God. The verse further confirms the existence of known statutes and laws of God prior to the giving of Israel’s laws by God on Mount Sinai (see also Genesis 26:5; Job 23:12). These primeval laws have now disappeared, though some remnants may have survived in other ancient legal codes (Hammurabi, Hittite, etc.). In any case, they have been superseded by the inspired system transmitted through Moses.
18:27 let his father in law depart. Moses had left his family with Jethro when he returned to Egypt to lead the Israelites to freedom. (Exodus 18:2). At this point, however, his wife Zipporah rejoined him, with their two sons Gershom and Eliezer (see Exodus 18:2-4). Apparently she had started with Moses to Egypt, but returned to Jethro after the circumcision of her son (Exodus 4:20,24-26). So far as the record goes, Zipporah thenceforth stayed with Moses and the Israelites.