(8) Then came Amalek, and fought with Israel in Rephidim. (9) And Moses said unto Joshua: ‘Choose us out men, and go out, fight with Amalek; tomorrow I will stand on the top of the hill with the rod of God in my hand.’ (10) So Joshua did as Moses had said to him, and fought with Amalek; and Moses, Aaron, and Hur went up to the top of the hill. (11) And it came to pass, when Moses held up his hand, that Israel prevailed; and when he let down his hand, Amalek prevailed. (12) But Moses’hands were heavy; and they took a stone, and put it under him, and he sat upon it; and Aaron and Hur held up his hands, the one on the one side, and the other on the other side; and his hands were steady until the going down of the sun. (13) And Joshua weakened Amalek and his people with the edge of the sword. (14) And the LORD said unto Moses: ‘Write this for a memorial in the book, and rehearse it in the ears of Joshua: for I will utterly blot out the remembrance of Amalek from under heaven.’ (15) And Moses built an altar, and called the name of it Hashem-nissi. (16) And he said: ‘The hand upon the throne of the LORD: the LORD will have war with Amalek from generation to generation.’

(18) Korcha (Smote) - comes from the expression "happenstance"(mikreh) ... A third possibility: This is the language of cool (kor) and heat, cooled you and stopped you from boiling. All the nations of the world were afraid to fight you [Israel] and this one came and started and showed the way to others. It is likened to a legend of a boiling bath that no creature could enter. A scoundrel came and jumped in. Even though he was scalded, he cooled it down for others.

Write this as a remembrance: The reason that we are commanded to wipe out the memory of Amalek is because they angered Hashem. The generals of Edom where trembling in fear because of the wonders that God wrought in Egypt and in the sea, as were the nations of Moav and the Philistines. When Amalek heard about the triumph of God for His nation Israel, they came from a distant land to fight with the Israelites, and they were not afraid of God.

Rabbi Yehoshua said to Rabban Gamliel: Do Ammon and Moab reside in their place? Sennacherib already came and, through his policy of population transfer, scrambled all the nations and settled other nations in place of Ammon. Consequently, the current residents of Ammon and Moab are not ethnic Ammonites and Moabites, as it is stated in reference to Sennacherib: “I have removed the bounds of the peoples, and have robbed their treasures, and have brought down as one mighty the inhabitants” (Isaiah 10:13).

(5) R. Levi declared: This situation may be compared to a child that is being carried on his father’s shoulders. When he sees something that excites him he calls out: “Father, take me there.” The father carries him to that place, and then to another and finally to a third place, yet the child, on seeing another man approaching them, asks: “Have you seen my father?” His father calls out: “You have been riding on my shoulders, and wherever you wished to go I carried you, yet now you ask ‘Have you seen my father?’” He then put him down. Whereupon a dog rushed at the child and bit him. Similarly, when the Israelites left Egypt, He surrounded them with clouds of glory, and when they wanted bread, He sent them manna, as it is said: And He caused manna to rain upon them for food, and He gave them of the corn of heaven (Ps. 78:24). And when they wanted meat, He gave them quail, as it is stated: They asked and He brought quails (ibid. 105:40). That is why it says: He gave them that which they craved (ibid. 78:29). And though He gave them whatever they demanded, yet they asked: Is the Lord among us or not? The Holy One, blessed be He, said to them: This is what you have been thinking. Therefore, this dog will bite you. Hence, And Amalek came.

You have to wipe out their memory in order to get revenge on them for Hashem.

Rabbi Levi says in the name of R' Hunah bar Hanina: As long as the seed of Amalek exists in the world, neither the Name (of the Lord) nor the Throne are complete. When the seed of Amalek has passed from the world, the Name and the Throne will be complete.

The core idea in the service of God is that a person should have no fear, as our rabbis (zichronam livrachah) taught us that in this world a person needs to walk on a very narrow bridge, and the most important thing is that this person should have no fear. The most important thing as a person is strengthening herself to walk across this narrow bridge in peace and without fear is the holy faith.