Amalek waged war against Israel and took back a captive from them.
Amalek first attacked the Jewish people when they were on the way to receive the Torah and again as they were preparing to enter the Land of Israel.
Similarly, our inner Amalek first attempts to cool our enthusiasm toward G-d and His Torah. As long as we are fulfilling our religious obligations, this might not seem to pose such a problem. But if we approach our Divine mission without warmth and enthusiasm, we will eventually lose interest in it, seeking diversions that offer more immediate material or spiritual gratification.
If our inner Amalek fails to cool our enthusiasm, it will attempt to take over our life in the "land," i.e., the material life we enter after our daily prayers and studies. It will argue, "Be holy while you're praying and studying the Torah, but when you're earning your living and dealing with the physical world, live by my rules."
Although this may sound like the voice of a clever businessman, we must recognize it as the voice of Amalek. Despite its concessions to our spiritual endeavors, its goal is to destroy us. The only proper response to Amalek is to wipe it out, by constantly renewing our enthusiasm for G-d and His Torah, and our desire that G-d be our guide in all aspects of life.
--From Kehot's Daily Wisdom