On Purim, the heavenly source of the soul is revealed, just as it is on Yom Kippur. On Purim, however, it is not revealed by means of fasting, but through feasting and rejoicing.

Purim is similar to Yom Kippur:

Purim and Yom Kippur are of the same essence. Purim is called by this name because of the lot, due to the pretensions of Haman, who “had cast a pur, which is the lot” (Esther 3:7), as he wanted to imitate the lot of Yom Kippur. And just as Yom Kippur contains supernal repentance: “Before the Lord you shall be purified” (Leviticus 16:30), so too, on Purim, the Jews merited supernal repentance through fasting and crying out, and being ready to give up their lives to sanctify God’s name. For Haman did not want anything other than to eradicate the Jews [those who live and believe according to the tenets of Judaism], and if they had, God forbid, denied their faith he would not have acted against them in any way. Accordingly, our Sages said (Shabbat 88a) that in the time of Ahashverosh they accepted the Torah willingly. As a result, their souls were raised up to the lofty source from which they were carved, through the aspects of “initial thought,” and “repentance preceded the world.” [Terms referring to the ability of repentance to elevate the soul to the most lofty source of existence. See Rashi, Genesis 1:1; Midrash Tehillim 90.]

The difference between Yom Kippur and Purim:

The revelation of this aspect of the soul on Yom Kippur [requires] not eating or drinking. But on Purim, which occurred during the exile, it is [revealed] specifically through the drinking of wine. Wine intoxicates, that is, it eliminates [normative and mundane] awareness and comprehension [thereby elevating the individual to a higher level]. (Rabbi Shneur Zalman of Liadi, Torah Or, Esther 95:4)