He sent word to Moses, “I, your father-in-law Jethro, am coming to you with your wife and her two sons.”
This incident may very well be allowed to have happened as it is placed here, before the giving of the law, and not, as some place it, in connection with what is recorded, Num 10:11, Num 10:29, etc. Sacrifices were offered before; in these mentioned here (Exo 18:12) it is observable that Jethro is said to take them, not Aaron.
Commenting on Exodus 18:1-6
And he said unto Moses,.... By a messenger, as Jarchi: or by a written letter, as Aben Ezra: or, as the Septuagint version, "it was told to Moses, thy father", &c. for as yet he was not come to him, as appears by Moses going forth to meet him: I thy father in law Jethro am come to thee: or, "am coming" (m); for, as...
and thy wife, and her two sons--See Exo 4:20.