This parshah mentions the avodah of the תרומת הדשן and הוצאת הדשן. The avodah of the תרומת הדשן was a mitzvah for the Kohen to shovel out ash from the inner coals of the mizbeiyach that were completely burnt, every day, and put it by the side of the mizbeiyach. This place was called מקום הדשן, which Onkelos translates as the place which ash was temporarily there. The Pas Shegen explains it was only temporary because Hashem performed a miracle that the ash was absorbed in its place. Rashi brings that in this place they put ash of the outer mizbeiyach, inner mizbeiyach, and Menorah, and the parts of the bird not burnt on the mizbeiyach. Hashem performed a miracle that all of the ash was absorbed in the ground. The Sifsei Chachamim adds that the Torah calls this place מקום הדשן, the place of the ash, hinting that the ash was absorbed there and it was only the place where the ash was put.
The הוצאת הדשן was when the Kohen removed ash from the mizbeiyach and brought it outside of the camp. This was not done every day, only when the ash piled up on the mizbeiyach and there was a need to make room. The Mishnah teaches that this mound was called תפוח because it was round as an apple, and it sometimes piled up to 300 kur! During the Yomim Tovim they left the ash there for the beauty of the mizbeiyach, publicizing that numerous korbanos were brought.
The passuk states that the Kohen shall dress מדו בד to perform the avodah of the תרומת הדשן. Rashi explains this refers to the tunic, one of the bigdei kehuna. Onkelos translates מדו בד as garments of linen, in plural, which the Ramban explains refers to all the bigdei kehuna. Since this was an avodah it required bigdei kehuna. After performing this avodah the passuk states, “ופשט את בגדיו ולבש בגדים אחרים and he shall remove his garments and wear other garments.” Rashi explains this is not an obligation, rather a proper thing to do. It is not fitting for a servant to cook for his master and then serve his master with the same clothes. So too the Kohen should not wear the regular bigdei kahuna which he uses for avodah, when he takes out ash, since they will become dirty. The Ramban understands that it is indeed an obligation to keep the bigdei kahuna which are designated for avodah clean. A Kohen should have beautiful garments to serve constantly, and other bigdei kehuna of lessor quality, to take out the ash.
May Hashem bring the Beis HaMikdah with the avodas Kohanim speedily in our days.