don't relinquish your power
Kedushas Levi
Purim
"Remeber what Amalek did to you... when you were tired and weary" (Devarim 25:17-18)
Not only are the descendents of Israel commanded to destroy the descendents of Amalek but also every individual Jew must eliminate that bad part hidden within his heart which is called Amalek. The Midrash actually calls a person a "small world" so the entire time that a remnant of Amalek exists, there also exists a power of evil in each and every one of us. This (internal force of Amalek) is always awake causing us to sin. This is why the Torah comes with this reminder.
The power of a Jew is with Torah and Mitzvos and when a person has this power, and his heart is always burning for the Creator, then no evil can can control him. But when a person relinquishes this power then immediately he weakens and Amalek comes, and evil dwells within him. Nonetheless, when a person takes hold of Yiras Hashem, and fears transgressing the Mitzvos, then (even if he is weak in Torah and Mitzvos), he will not come to sin.
This is why the verse says "You were tired and weary", you are lacking the power of a Jew because you have weakened in serving Hashem. And it also says "You did not fear Hashem," you must always be careful to remember not to stumble because of the power of Amalek. So the Torah tells us "you will eliminate" from your heart the root of evil and subjugate (your heart) to the good.
