The Talmud: Selections, by H. Polano, , at sacred-texts.com
This festival, occurring on the fourteenth day of the twelfth month, Adar (March), is to commemorate the deliverance of the Hebrews from the wiles of Haman, through the God-aided means of Mordecai and Esther.
Although the Holy One threatens the Israelites, in order that they may repent of their sins, He has also tempted them, in order to increase their reward.
For instance, a father who loves his son, and desires him to improve his conduct, must punish him for his misdeeds; but it is a punishment induced by affection which he bestows.
A certain apostate once said to Rabbi Saphra:
"It is written, 'Because I know you more than all the nations of the earth, therefore I visit upon you your iniquities;'
how is this? If a person has a wild horse, is it likely that he would put his dearest friend upon it, that he might be thrown and hurt?"
Rabbi Saphra answered:
"Suppose a man lends money to two persons; one of these is his friend, the other his enemy. He will allow his friend to repay him in instalments, that the discharge of the debt may not prove onerous; but from his enemy he will require the amount in full. The verse you quote will apply in the same manner, 'I love you, therefore will I visit upon you your iniquities;' meaning, 'I will punish you for them as they occur, little by little, by which means you may have quittance and happiness in the world to come.'
The action of the king in delivering his signet ring to Haman had more effect upon the Jews than the precepts and warnings of forty-eight prophets who lectured to them early and late. They clothed themselves in sackcloth, and repented truly with tears and fasting, and God had compassion upon them and destroyed Haman.
Although the reading of the Book of Esther (Megilah) on Purim is not a precept of the Pentateuch, ‘tis nevertheless binding upon us and our descendants. Therefore the day is appointed as one of feasting and gladness, and interchange of presents, and also of gifts to the poor, that they too may rejoice. As in the decree of Haman, no distinction was made between rich and poor, as all alike were doomed to destruction, it is proper that all should have equal cause to feel joyful, and therefore in all generations the poor should be liberally remembered on this day.