Exodus 17:8 - Ellicott's Commentary On The Whole Bible

Then came Amalek. — The Amalekites had not been previously (except in the anticipatory notice of Genesis 14:7) mentioned as a nation. Their name marks them for descendants of Amalek, the grandson of Esau (Genesis 36:12; Genesis 36:16); and it would seem that they early became the predominant people in the Sinaitic peninsula. Balaam speaks of them as “the first of the nations” (Numbers 24:20); and though we do lot meet with the name in the Egyptian records, yet it is probable that they were among the hostile nations whom we find constantly contending with the Egyptians upon their north-eastern frontier. Though Edomitesn they are always regarded as a distinct race, and one especially hostile to Israel (Exodus 17:16). Their present hostility was not altogether unprovoked. No doubt they regarded the Sinaitic region as their own, and as the most valuable portion of their territory, since it contained their summer and autumn pastures. During their absence in its more northern portion, where there was pasture for their flocks after the spring rains, a swarm of emigrants had occupied some of their best lands, and threatened to seize the remainder. Naturally, they would resent the occupation. They would not understand that it was only temporary. They would regard the Israelites as intruders, robbers, persons entitled to scant favour at their hands. Accordingly, they swooped upon them without mercy, attacked their rear as they were upon the march, cut off their stragglers, and slew many that were “feeble, faint, and weary” (Deuteronomy 25:17-18). They then encamped in their neighbourhood, with the design of renewing the struggle on the next day. It was under these circumstances that Moses had to make his arrangements.