The festive Purim meal has special significance, for it elevates the soul as well as providing pleasure for the body. The Zohar writes that on Purim one can achieve the same spiritual elevation with bodily pleasure that one accomplishes on Yom Kippur by afflicting the body.
The people of Israel are holy, physically as well as spiritually. Thus, it is fitting that Israel's physical actions be imbued with holiness, and that they be performed so as to sanctify and serve as praise of G‑d. Our Sages maintained that G‑d's praise is greater when it comes from the physical realm rather than from the spiritual realm.
However, as long as Amalek exists, they corrupt the purity of Israel's actions and pollute them by introducing an element of sin into them. When Amalek's powers are weakened and they are subjugated, then Israel's physical actions are immediately imbued with purity and they are performed for G‑d's sake alone - from this G‑d's praise results.
The joy associated with the mitzvah of this festive Purim meal is especially great, for it signifies that Israel has rectified the sin which they were culpable for during the time of Haman: participating in the feast of Achashverosh.
Had this sin not been totally rectified, they would have been required to atone for it by subjecting themselves to affliction. The fact that they have been commanded to bring themselves physical pleasure serves as a sign that they no longer bear a remnant of guilt for this sin. Moreover, they have purified their bodies and their actions to the point where it now becomes incumbent upon them to bring themselves physical pleasure through eating and drinking.
It is proper to engage in some Torah study before beginning the festive Purim meal. This is alluded to in the Megillah, for the verse states: "The Jews had light and festivity (Esther 8:16)". The Sages explained: light - this refers to the Torah.