Fasting on Yom Kippur (the Day of Atonement) symbolizes that we restrict our broken desires and are ready to use them only for the sake of bestowal. If the desires are corrupted, then their correction begins with a Tzimtzum (restriction), with the condition that we do not accept any Light if there is no intention to bestow to my neighbor.
I will be able to use my desire for the benefit of others if I stop receiving for a “full day,” and then I can again return to receiving the Light. This means that I have passed a full stage detached from receiving, in restriction, and now I can receive the Light again, for the sake of bestowal. In the spiritual world, this action takes place on every new stage.1
We exist in the full HaVaYaH, the five Sefirot: Keter, Hochma, Bina, Zeir Anpin, and Malchut. If you cut off all the particular Sefirot of Malchut from them, then the remaining Kelim can be used. Therefore, on Yom Kippur there are five restrictions against Keter, Hochma, Bina, Zeir Anpin, and Malchut: a ban on food, drinking, intimacy, bathing, and wearing leather shoes. Everything else is our internal thoughts and desires and a calculation should be made there not to receive for one’s own sake.
This means that you make a restriction and so move yourself through the “judgment.” Yom Kippur is the day of judgment.2
From the 3rd part of the Daily Kabbalah Lesson 9/18/18, Writings of Baal HaSulam, Shamati 69 “First Will Be the Correction of the World”
1 Minute 28:45
2 Minute 37:20