Once a year, the High Priest would enter the Holy of Holies in the Tabernacle (later the Temple) where he would offer sacrifices for the nation of Israel (Exodus 30:10; Lev. 16; Num. 18:2,5,7; Heb. 8:3; 9:7). He would sprinkle blood on the Mercy Seat which was actually a lid on top of the Ark of the Covenant.