This piece was originally written in 5777/2016.
The Sfat Emet has many teachings about Sukkot which intersect well with his description of Yom Kippur as being like a mikvah.
We are required to dwell in the Sukkah for the seven days of the holiday of Sukkot (as well as Shemini Atzeret, which many Hasidic masters liken to the very pinnacle of the festival because it’s the day that God devotes especially for the Jewish people because there’s the one sacrifice, rather than the seventy bulls for Sukkot).
In many respects, the sukkah serves a similar function as a mikvah spiritually-speaking. Just as we are wholly immersed in the grandeur, ritual, spirituality and prayer of Yom Kippur, so, too, when we are rejoicing in the sukkah as we are commanded to do, so, too, is our physical body wholly immersed in the act of rejoicing. This act of rejoicing is as spiritually significant as is the act of contrition and repentance. The Sfat Emet teaches us that dwelling in the Sukkah is quite literally dwelling with God. The divine dwells in the Sukkah, so, too, are we truly unified with God. The Sfat Emet is very interested and concerned with achieving this divine mystical union with the Holy One. The sukkah is a flimsy physical structure but dwelling within it allows us to reach greater spiritual heights. When Sukkot is upon us, we have passed through the awesomeness of the Yamim Noraim, but yet are still very aware of our fragility, as is exemplified by the hoshanot. We are holding two emotions at once—fragility and joy. We sing Hallel joyfully, and engage in the supplications of the hoshanot. Thus, this results in us yearning for that total union with God, which the Sfat Emet teaches us we achieve when we dwell in the sukkah. That dwelling is something that is available to all Jews, not merely the tzadikim. Therefore, it is radically decentralized—God is quite literally in our dwelling places. We are always aspiring to greater spiritual unity and wholeness.