The Tanya teaches us that when one sins, HaShem nourishes us externally from an infinite distance known as makif, (translated as surrounding) in other words, when we transgress His desires, He still nourishes us with life, but will have no part in it directly. Conversely when we perform mitzwoth, as we've mentioned in the past, we have the oppurtunity to create a dwelling place for HaShem within those actions, and within ourselves.
When we sin we also take of the life-force that HaShem has given us and use it to perform these nefarious deeds.
So, when we do Teshuvah, we find that we are actually rectifying two kinds of divine light. The small trickle of life force that was within us when we performed the sin, and the surrounding makif light that was the essence of our relationship with HaShem at that moment.
We spoke about the small inner life force, when we understood that it is this which becomes the cloud through which we are able to perceive HaShem. (כי בענן אראה על הכפרת)
What we didn't talk about was what happens to the rectified makif light when we do Teshuvah. It too is turned into a cloud, but in this case the cloud is a surrounding (makif) cloud. The Teshuvah of Bnei Yisrael is the source of the ענני הכבוד - the Clouds of Glory that surrounded Bnei Yisrael and protected them in the desert. These are the clouds that the Sukkah represents.
This is why Yom Kippur comes after Sukkoth, so that the rectification of our past transgressions complete the clouds of glory of the Sukkah. On Sukkoth we sit surrounded and protected by the product of our refined sins. (This is a hidden meaning of - במקום שבעלי תשובה עומדים אין צדיקים גמורים יכולים לעמוד - the Sukkah of a Ba'al Teshuvah is different than the Sukkah of a Tzaddik Gamur.)