The Shabbat before Purim is Shabbat Zahor, a Shabbat of Rememberance. Remember to erase the name of Amalek for what he did to us in the desert when we left Egypt, attacking the very weakest and most vulnerable. Remember that in every generation there is an Amalek, a man without compassion. The Scroll of Esther (Megillat Esther), is read on Purim. In it the evil Haman is reported to be the descendent of Amalek. Rememberance is the key to overcoming the evils of the past, to preventing their reoccurrence. It is a powerful generator for repentance and reconcilliation.
The Fast of Esther, on the day before Purim is a time to confront suffering, a time to honor victims, a time to remember what it means to be vulnerable. By remembering we can distinguish between the different types and levels of evil. Forgiveness is sometimes possible for the individual, even if not for the act. But the Talmud warns us whoever is compassionate to those who deserve cruelty ends up being cruel to those who deserve compassion.
Our suffering must not make us arrogant and self righteous in our victories. Our very bodies were marked for destruction, we must therefore celebrate them and all life now. Gd is not mentioned in the Megillah. Gd is revealed to us in the miracle of the world around us. "When Gd dispatches angels to do his bidding, they take the form of fires, winning lottery tickets, business upturns, winds that push balls over goal posts, aggressors - the entire panoply of causes and effects that make headlines and history books. We are always challenged to see the Hand inside the glove" of what we call nature. "Only if we acknowledge Gd in every happening does Divine Providence manifest in everything". (1)
We give, on Purim, an edible gift of two kinds of food to at least one friend, though many give to a long list. Giving tzedakah on the day of Purim is a key part of the festival. "The mitzvah of giving tzedakah on Purim is scupulously kept by Gd and he dispenses tzedakah to anyone that asks".(2) Give to anyone who asks, or to at least two persons in need. And open your heart in prayer, asking Gd to answer yours.
It is a mitzvah to have a festive meal and to fill ourselves with delicious food and wine. Our Sages have commanded us to get drunk on Purim in order to attain a different state of mind. We drink until we do not know the difference between the Blessed Mordechai, Esther's Uncle, and the Cursed Haman. On Purim things are not what they appear to be. In fact everything is it's opposite. "Purim is the model of paradox. Purim demonstrates that our assumptions of reality can suddenly be overturned. It is the sudden juxtaposition of two opposites, which shed a new light on the whole".(3)

Illustration by Juan Wijngaard from "Esther's Story" by Diane Wolkstein
"The Jewish Way" Rabbi Irving Greenberg
"Seasons of Our Joy" Aurthur I Waskow
"Purim - It's Observance and Significance" Compiled by Rabbi Avie Gold p 18-20 (1)
Pri Tzaddik quoted in the article "Eis Ratzon" from The Jewish Observer, Feb 1993 (2)
Eliezer Shore for A Still Small Voice, Holiday Supplement for Purim 1988 (3)