John Calvin on Exodus 17:13

13. And Joshua discomfited Amalek. The copula is here used instead of the illative particle; for Moses here concludes that the Israelites overcame their enemies, because he had continually persevered in prayer. There is, too, an implied antithesis between the firmness of his hands and the weakness of the enemy, that we may know that they were discomfited or conquered, not so much by the sword as by the uplifting of the rod, and by the intercession of the holy man.