Yom Kippur and th 15th of Av were once days when young maidens would dance in the vineyards for their would be suitors who would witness the spectacle. We were told that these were the most joyous of days. Rav Nachman of Breslav, the great Hasidic master sees the fast itself as reason for celebration. Yom Kippur magically includes all the days of the year which is why it has the power to atone for all of them. Fasting on this day, revives the days we have slain through our sins, and this makes sense biologically:
One can understand this from a material perspective. When one fasts, it is as if one does not have sustenance and strength from that day because he has neither eaten nor drunk anything, and still, he is serving God. It must be that there is strength left over from yesterday. Thus he is bringing the strength of yesterday to today, and when he continues to fast, there isn’t enough from yesterday to sustain him so he must go further in the past, and through this he brings life back to the fallen and dead days and through this, he brings forth light and life to all the days.
Fasting diminishes desire so that we can fill ourselves with the glory of God. It is an opportunity to be welcomed. He has much more to say on this and I have posted a translation of the essay in its entirety. For the Hebrew and English, Rav Nachman on Yom Kippur click here