Charles Ellicott Commentary Exodus 17:10

"So Joshua did as Moses had said to him, and fought with Amalek: and Moses, Aaron, and Hur went up to the top of the hill." — Exodus 17:10 (ASV)

Moses, Aaron, and Hur went up. —Moses, we know, was eighty years of age (Exodus 7:7); Aaron was eighty-three; Hur, the grandfather of Bezaleel (Exodus 31:2), the architect of the Tabernacle, can scarcely have been younger. Unfit for battle themselves, they felt it was by prayer and intercession that they could best help bring about a good result, and so they withdrew from the actual conflict to a place where they could oversee it.

Hur. —According to Jewish tradition (Josephus, Antiquities of the Jews, iii. 2, § 4), Hur was the husband of Miriam, and thus the brother-in-law of Moses and Aaron. He was a descendant of Judah through Pharez and Hezron (1 Chronicles 2:3–20). Moses left him as joint regent with Aaron when he ascended Sinai (Exodus 24:14).