Moses kept the flock. The Hebrew expresses that this was his regular occupation. Understand by "flock" either sheep or goats, or the two intermixed. Both anciently and at the present day the Sinaitic pastures support these animals, and not horned cattle.
Of Jethro, his father-in-law. The word translated "father-in-law" is of much wider application, being used of almost any relation by marriage. Zipporah uses it of Moses in Exodus 4:25, Exodus 4:26; in Genesis 19:12, Genesis 19:14, it is applied to Lot's "sons-in-law;" in other places it is used of "brothers-in-law."
Its application to Jethro does not prove him to be the same person as Reuel, which the difference of name renders improbable. He was no doubt the head of the tribe at this period, having succeeded to that dignity, and to the priesthood, when Reuel died.
He may have been either Reuel's son or his nephew. The backside of the desert, i.e. "behind" or "beyond the desert," across the strip of sandy plain which separates the coast of the Elanitic Gulf from the mountains, to the grassy regions beyond.
He came to the mountain of God, even Horeb. Rather, "the mountain of God, Horeb-way," or "towards Horeb." By "the mountain of God" Sinai seems to be meant. It may be so named either by anticipation (as "the land of Rameses" in Genesis 47:11), or because there was already a sanctuary there to the true God, whom Reuel and Jethro worshipped (Exodus 18:12).