Since many Hebrew people rejected the new covenant of grace, including many of the priests, the priests continued the daily and yearly sacrifices of animals for the sins of the people (Hebrews 10:11).
The work of the priests under the old covenant was never finished.
They stood day after day and year after year sacrificing animals to cover their own sins and the sins of the people.
They could never rest (Hebrews 10:11).
There was always another animal to be sacrificed to cover their own sins and the sins of others (Hebrews 5:1-3).