While the first seven days of the Mishkan were a "dry run" where Moshe had to do everything, the eighth day was the start of the actual mission. On this day, the Kohanim were empowered to take ownership of their service. Moshe dressed them only in the Ketonot to initiate their status, leaving the rest to them. However, for Aharon the High Priest, whose service brought the Infinite Light into the Tabernacle, Moshe remained fully involved, dressing him in every garment to ensure the Shechinah found its permanent home.

https://www.torahrecordings.com/likutei-sichos/026/016_003