the Sacred Vail: The High Priest: Could not Enter Without Blood
Source: TTT
Leviticus 16:3
This is how Aaron is to enter the Holy Place: with a young bull for a sin offering and a ram for a burnt offering.
Hebrews 9:7
But only the high priest entered the second room, and then only once a year, and never without blood, which he offered for himself and for the sins the people had committed in ignorance.