Albert Barnes Commentary Exodus 17:9

"And Moses said unto Joshua, Choose us out men, and go out, fight with Amalek: to-morrow I will stand on the top of the hill with the rod of God in my hand." — Exodus 17:9 (ASV)

Joshua - This is the first mention of the great follower and successor of Moses. He died at the age of 110, some 65 years after this transaction. His original name was Hosea, but Moses calls him by the full name, which was first given about forty years afterward, as the name by which he was to be known to succeeding generations. From this it may perhaps be inferred that this portion of Exodus was written, or revised, toward the end of the sojourn in the wilderness.

The rod of God - See (Exodus 4:20). The hill is supposed to be the height now called Feria on the north side of the plain Er Rahah (or, Jebel Tahuneh over Feiran. Palmer).