The 8 items of clothing worn by the Kohen Gadol are divided into 2 categories;
Bigdei Zahav: 4 coloured garments that had gold in them; the Tzitz (head-plate), Ephod (apron), Choshen (breast-plate) and Me’il (robe).
Bigdei Lavan: - 4 garments of white linen; the Mitznefes (turban), Kesones (tunic), Michnasayim (breeches) and Avneit (sash).
The Ariza”l explains that the 4 white garments correspond to the 4 letters of the Name י-ה-ו-ה, which represents G-dliness that is beyond the worlds. The 4 golden garments correspond to the 4 letters of the name אדנ-י, representing the concealment of G-dliness within the veil of nature.
Wearing the combination of the 2 sets of garments reflects how the transcendent light of י-ה-ו-ה is enclothed and hidden within אדנ-י.
The Kohen Gadol wore these 8 garments every day of the year. But on Yom Kippur, when entering the Holy of Holies, the Kohen Gadol only wore 4 white linen garments, representing a pure revelation of transcendent G-dliness that is not hidden within nature.
Our day-to-day Avodah is to engage with the world through our physical activities, to draw down G-dliness. This is like wearing the combination of the gold and white garments.
But from time-to-time, we need the Yom Kippur experience; moments of spiritual elevation and inspiration where we rise completely beyond physicality, like Yom Kippur when we fast, negating our body as we ascend into the Holy of Holies of our souls. This gives us the strength to come back into the world to uplift it.
On a daily level, this is when we enter the Holy of Holies of prayer, where we rise above the world to connect with our soul. Once we have connected Above, we can put on the golden garments as we set out to bring this connection into the world and every aspect of our daily life.