- On exactly the tenth day of this seventh month is the day of atonement (Yom Kippur); - Leviticus 23:27
On the Day of Atonement, the high priest offered the Sin Offering on behalf of the whole nation. The blood of a slaughtered goats was sprinkled on the Mercy Seat (kappōret — the place of propitiation).
- Then he shall slaughter the goat of the sin offering which is for the people, and bring its blood inside the veil and [...] sprinkle it on the mercy seat (kappōret)... - Leviticus 16:15
The Mercy Seat was representative of God’s throne in Heaven, where He sits. When the blood was sprinkled on the Mercy Seat, God saw it as a covering for sin and thus extended mercy to those represented by the blood. Interestingly, the Greek term for propitiation (hilastērion) means the place of propitiation and directly translates the Hebrew term kappōret or Mercy Seat.
- and above it were the cherubim of glory overshadowing the mercy seat (hilastērion); but of these things we cannot now speak in detail. - Hebrews 9:5
Propitiation, then, means to cover a wrong that has been committed. It speaks to how God is completely satisfied with Christ’s sacrifice. By enduring the humiliation, Jesus became a merciful and faithful high priest. Though eternally the Son of God, Jesus took on the ministry of High Priest at His death. He is merciful in His dealing with humanity. He is faithful in the observance of His priestly duties. By becoming a High Priest, He is able to make propitiation for the sins of the people.
- Therefore, He had to be made like His brethren in all things, so that He might become to make propitiation for the sins of the people. - Hebrews 2:17