Though Esau himself was full of bitter hatred, and Ishmael is described as a wild man, Amalek seems to have been the worst of the Edomite-related peoples. The Bible records that even God has a special enmity for Amalek, saying in Exodus 17:16, "Because the LORD has sworn: the LORD will have war with Amalek from generation to generation." What is it about the Amalekites that turns God against them?
The story begins as the Israelites are fleeing from Egypt, having just crossed the Red Sea, as Exodus 17:8 chronicles, "Now Amalek came and fought with Israel in Rephidim." Evidently, the Amalekites had heard of Egypt's total defeat at the Red Sea and decided to take advantage of its usually more powerful neighbor's weakness. Between them and their prize, however, walked a strung out line of Israelite wanderers, who seemed to be, not only laden with Egyptian loot, but also easy pickings.
Deuteronomy 25:17-18 fills out the story: "Remember what Amalek did to you on the way as you were coming out of Egypt, how he met you on the way and attacked your rear ranks, all the stragglers at your rear, when you were tired and weary; and he did not fear God." The Amalekites, not daring to take on the main host of Israel, attacked the tail end of the line, where the slow and weak plodded along. Yet, as Moses notes, the Amalekites did not include God in their calculations.
Moses commanded Joshua to select men to fight, and the Israelites met the Amalekites in battle. The result of this seesaw fight appears in Exodus 17:13-16. Forty years later, when Israel is about to cross over Jordan, God reminds Israel of Amalek's perfidious act and charges them:
Therefore it shall be, when the LORD your God has given you rest from your enemies all around, in the land which the LORD your God is giving you to possess as an inheritance, that you will blot out the remembrance of Amalek from under heaven. You shall not forget. (Deuteronomy 25:19)
The Amalekites appear again in the well-known episode in which God instructed King Saul to carry out this command:
Thus says the LORD of hosts: "I will punish Amalek for what he did to Israel, how he ambushed him on the way when he came up from Egypt. Now go and attack Amalek, and utterly destroy all that they have, and do not spare them. But kill both man and woman, infant and nursing child, ox and sheep, camel and donkey." (I Samuel 15:2-3)
However, despite winning the battle, Saul did not follow God's instructions completely: "But Saul and the people spared Agag [king of the Amalekites] and the best of the sheep, the oxen, the fatlings, the lambs, and all that was good, and were unwilling to destroy them. But everything despised and worthless, that they utterly destroyed" (verse 9). God sent the prophet Samuel to tell Saul that He had rejected him as king, as well as to execute Agag.
Obviously, some Amalekites escaped Saul's army. Five centuries later, as recorded in the story of Esther, an evil man named Haman plotted genocide against the Jews in Persia during the reign of Xerxes. Haman was "the son of Hammedatha the Agagite" (Esther 3:1), probably directly descended from the Amalekite king Samuel killed.
These accounts relate the sort of trickery, terrorism, and underhandedness that the Amalekites seem to use perpetually. One can only conclude that these tactics are passed from generation to generation, becoming a hereditary trait. God has recorded these episodes to indicate to us how Amalek historically treats Israel. If a confederacy is formed against Israel, the Amalekites will be a part of it, and they will be eager to use any means to bring her down.