Remember what Amalek did to you on the road, on your way out of Egypt. That he encountered you on the way (Deuteronomy 25:17-18)
[The Hebrew word karcha, "encountered you," also translates "cooled you off". Thus the Midrash says:]
What is the incident (of Amalek) comparable to? To a boiling tub of water which no creature was able to enter. Along came one evil-doer and jumped into it. Although he was burned, he cooled it for the others.
So, too, when Israel came out of Egypt, and G‑d rent the sea before them and drowned the Egyptians within it, the fear of them fell upon all the nations. But when Amalek came and challenged them, although he received his due from them, he cooled the awe of them for the nations of the world.
Amalek is thus the essence of chutzpa, of completely irrational challenge to truth. There are challenges to the truth that are based on rational argument. There are evasions that arise from subjective motives and desires. But then there is "Amalek," who neutralizes the most compelling evidence and chills the most inspiring experience with nothing more than his cynicism and audacity.
There is only one way to defeat Amalek: to remember. Because his challenge is not rational, it cannot be rationally refuted; because it immune to feeling, it cannot be repelled by a rousing of emotion. To counteract Amalek's poison, one must call forth the souls reserves of supra-rational faith, instilled within it when it was first formed as a spark of the divine essence—a faith which, when remembered, can meet his every moral challenge.
(The Chassidic Masters)