Clothing was first introduced after the sin of the Tree of Knowledge, when Adam and Chava realised they were unclothed and Hashem made them כתנות עור, “garments of skin”. The Midrash teaches that in the Torah of Rabbi Meir these words are written as כתנות אור (with an Alef), meaning “garments of light”.
Chassidus explains that both are true. Before the sin they had “garments of light”. After the sin they were replaced with “garments of skin”.
Before the sin, physicality did not conceal G-dliness and the physical body did not hide the light of the Neshama. This is like the translucent “garments of light” that allow light and holiness to shine through. As a result of the sin, physicality became corrupted so that it became oppositional and concealed G-dliness. This is the opaque “garments of skin”.
The Beis Hamikdash was a microcosm of Gan Eden, a place where G-dliness was openly manifest and physicality itself radiated holiness. In this space, the garments of the Kohanim are called Bigdei Kodesh, holy garments that reveal holiness like the “garments of light”.
Tanya teaches that our thoughts, speech and actions are like garments. The thoughts, speech and action that express our Animalistic Soul are “garments of skin”, which hide the light of our Neshama and bring further concealment to the world.
When we serve Hashem with the thoughts, speech and action of Torah and Mitzvos which express our G-dly soul, we are like the Kohanim serving in the Beis Hamikdash. These are Bigdei Kodesh, “garments of light” that enable our Neshama to shine forth.
With these ‘garments’ we also refine the physicality of the world, bringing it one step closer to Moshiach when once again physicality will reveal G-dliness, just as it did in Gan Eden and in the Beis Hamikdash.