On Shabbat before Purim in addition to the regular Torah reading we read a small paragraph from the end of parashat "Ki Teitzeh". "Zachor Et Asher Asa Lecha Amalek BaDerech Betzetchem MiMitzrayim", "Remember what Amalek did to you on your way out of
The day of Shabbat includes the whole coming week in itself. (Every day during the Morning Prayer, Shacharit, we say "היום־יום־שלישי־בשבת־קודש" “today is the third day of the Holy Shabbat”. We also announce the new moon on Shabbat. The short paragraph of Zachor gives us the ability to overcome doubts, (Amalek in Gimatria equal doubts) "עמלק־=ספק", and have certainty in our connection to the Light. Purim is a celebration of certainty. Mordechai and Esther were thinking about G-d and not the people. Mordechai risked his life and the life of all Jews when he refused to bow to Haman Hagagi. Because of their certainty, they merited the miracle of overcoming Haman.
It is important to know that Haman was a descendent of Amalek. Shemuel the prophet ordered King Saul to kill Agag, the King of Amalek and all that belonged to him. King Saul failed by keeping some goods as offerings to G-d and he brought Agag as prisoner. Agag was killed by Shemuel but before that he had the opportunity to be with a woman and have a child who continued the line of Amalek all the way to Haman. Mordechai succeeded to destroy Haman and his ten sons (representing the 10 levels of negativity and that is why the reader of the megilah needs to read their names in one breath).
Zachor is also a reminder of the final redemption, when G-d promised to remove Amalek for ever and that means no negativity ever again. Rabbi Avraham Azulai, in the book "Chessed L\’Avraham" said that the final redemption is a state that is better than what the Garden of Eden was, before the sin. The reason for that is, before the sin, the Snake was there and had the potential to harm and eventually he did. In the final redemption, there will be no negativity. B"H we will all merit seeing Mashiach and the final redemption, today, Amen.