But every priest stands daily ministering and repetitively offering the same sacrifices, which can never take away sins. But this Man, after He had offered one sacrifice for sins forever, sat down at the right hand of God.
— Hebrews 10:11-12
Only the High Priest could enter into the Holy of Holies, and that but once a year, and then not without the blood of the sacrifice that was to be sprinkled onto the mercy seat.
What was in that Holy of Holies? There was the Ark of the Covenant. Within it were found the two tables of the Law written by the very hand of Jehovah. Those laws, looking upward, cried out against the transgressions of men against the commandments. On the top of the Ark was the mercy seat, covered in pure gold. Once a year on Yom Kippur, the Day of Atonement, the High Priest entered into the Holy of Holies and sprinkled blood on the mercy seat of the atonement.
On either end of that Ark, gold-covered cherubim faced inward. Between those cherubim there dwelt the presence of the Almighty God. There the broken law cried out for vengeance upon the transgressors, and it was only the blood of the atonement that blocked it out. That is a great picture of Christ who entered the Holy of Holies in Heaven itself with His own blood to make atonement for our sins. There is the secret place of the most High God, where mercy is meted out through the death of the Sacrifice.