The War with Amalek at Rephidim
Amalek attacks the exhausted people; Joshua leads the fight, Moses holds up his hands, and remembering Amalek becomes a commandment.
At Rephidim, soon after the Exodus, Amalek — a descendant of Esau — attacked Israel. He was defending no territory and demanding nothing: he struck the tail of the column, where the weary and the stragglers walked. Moses gave the battle to Joshua son of Nun, who appears here for the first time in the Torah, and himself climbed a hill with the staff in his hand. While Moses' hands were raised Israel prevailed; when they dropped, Amalek did. His hands grew heavy, so Aaron and Hur sat beside him and held them up until sunset. Joshua defeated Amalek, and God commanded that this be written in a book. Two commandments grew from the episode — to remember what Amalek did and to blot out his memory — read in synagogue on the Sabbath before Purim, since Haman is traditionally a descendant of Amalek. Amalek names a kind of cruelty that has no aim and no profit, and therefore cannot be negotiated with.