Into the holiest place
During biblical times Yom Kippur was the only day on which the High Priest could enter the inner sanctum of the Holy Temple in Jerusalem – the Holy of Holies. There, before the Ark of the Covenant, he would perform a series of rituals and sprinkle blood from sacrificed animals on the Mercy Seat of the Ark, which contained the Ten Commandments, a bowl of manna and Aaron's staff.
Through this complex ceremony, the High Priest sought God’s forgiveness on behalf of Israel. The tradition is said to have continued until the destruction of the Second Temple by the Romans in 70 A.D; it was then adapted into a service for rabbis and their congregations in individual synagogues.