Any Old Rubbish
If you think about it, a succah is a peculiar thing. We take great pains to deck it out so that it becomes our home away from home. We take in our finest tableware and furnishings. We bedeck it like a princess with all manner of jewelry and decoration. And yet look up at the roof of a succah and what do you see? Rubbish. Dead palm fronds. "The chaff of the vineyard and the granary."
It's difficult for us to visualize spiritual realities. We know that on Yom Kippur, if we merit it, all our sins are forgiven. We emerge from synagogue white as snow (hopefully, not from lack of food.)
But not only does Hashem forgive our errors, if we do teshuva out of love, our sins are turned into mitzvot.
This is a very difficult concept for us to grasp, and maybe even as we sit in our succot we may feel a twinge of sadness. Can my sins really become mitzvot?
At that moment we can look up and see a perfect visual-aids representation of sins being turned into mitzvot. The schach, the rubbish which is the ceiling of our succah, is its essential part. The word succah comes from schach. Waste and rubbish have been turned into a mitzvah of incomparable spiritual beauty, outshining by far the brightest decoration and adornment. Now we can understand: Teshuva that comes from love turns our "rubbish" into mitzvot.
- Source: Rabbi Yissochar Dov Turnheim