Moses’ hands were heavy. — Moses writes with a clear remembrance of his feelings at the time. His hands, long stretched to heaven, grew weary, “heavy,” feeble; he could no longer raise them up, much less stretch them out, by his own muscular energy. They sank down, and dropped by his sides. If the battle was not to be lost, it was necessary to find some remedy. Apparently, Aaron and Hur bethought themselves of an effective remedy, none being suggested by Moses.
They took a stone. — Partly to give him a certain amount of rest, but, perhaps, mainly to enable them the better to sustain his hands. The fact is one of those “little” ones, which none but one engaged in the transactions would have been likely to have been acquainted with. (See “Introduction,” § 5)
Aaron and Hur stayed up his hands. — Left to himself, Moses had become exhausted both mentally and bodily, and when his hands dropped, had ceased to pray. Sustained physically by his two companions, his mind recovered itself, and was able to renew its supplications and continue them. The result was the victory.