Deuteronomy 25:17

17.Remember what Amalek did unto thee. We have elsewhere seen how the Amalekites were the first who made a hostile attack upon the people, and endeavored to interrupt their journey; and Moses also related the sentence of God against them, the execution of which he now enjoins upon the people. God then swore that there should be perpetual war against them throughout all ages; and, that His threatening might not be frustrated, He appoints His people to take vengeance upon their great cruelty and impiety. For when the Israelites were inflicting no injury nor loss upon them, it was an act of injustice to make war upon peaceful persons proceeding, without doing any wrong, to another land. But humanity was still more grossly violated by them, inasmuch as they did not spare their own kindred, and thus cast away the feelings of nature. It is plain from Genesis 36:12, that the Amalekites were the descendants of Esau; and hence it follows that they were both sprung from the same ancestor, Isaac. It is true that this command seems but little in accordance with religion, that the people should retaliate an injury done to them. I reply, that they are not stimulated to vindictive feelings in these words, but that they are commanded to punish the sins of Amalek with the same severity as those of the other nations. God appears, indeed, to influence them by private motives when He recounts the cruelty shewn by the Amalekites; but we must judge of the intention of the Legislator with reference to His nature, for we know that no angry or hateful passions can be approved by God; and hence it is easy to conclude that the command was such as the people might obey with well-regulated zeal. The first origin of the crime is specified, viz., because they “feared not God,” for this must not be taken in its ordinary meaning, but as expressing that they rebelled against God as it were deliberately. For the promise given to Abraham and Isaac could not be unknown to them; but, since Esau, the founder of their race, had fallen from the right of primogeniture, it came to pass that they attempted to bring God’s covenant to nought out of wicked and sacrilegious jealousy; and this is the reason why He unites them with the reprobate nations unto the same destruction. The word זנב, zineb, which means to crop the tail, is equivalent to making an attack on the rear, where the baggage and invalids are wont to be placed. (304)