Orthodox Apologetics

Third, the word hilasterion, which I have translated as the substantive “expiatory,” seems to have in Paul’s mind a more technical significance. In Hebrews 9:5, the only other place where the word appears in the New Testament, hilasterion designates the top, the cover, of the Ark of the Covenant, where the Almighty is said to throne between and above the Cherubim. In this context, the term is often translated as “mercy seat,” and it seems reasonable to think that this is the image that Paul too has in mind.
On Yom Kippur, the annual Atonement Day, the high priest sprinkled sacrificial blood on that hilasterion,
“because of the uncleanness of the children of Israel, and because of their transgressions of all their sins” (Leviticus 16:16).
Therefore, by saying that God “set forth” (proetheto) Jesus as the expiatory, or “instrument of expiation,” for our sins, Paul asserts that the shedding of Jesus’ blood on the Cross fulfilled the prophetic meaning and promise of that ancient liturgical institution of Israel, reconciling mankind by the removal of the uncleanness,
“their transgressions of all their sins.”
The Cross was the supreme altar, and Good Friday was preeminently the Day of the Atonement. The removal of sins was not accomplished by a juridical act, but a liturgical act performed in great love:
“Christ also has loved us and given Himself for us, an offering and a sacrifice to God for a sweet-smelling aroma” (Ephesians 5:2).
Loving both the Father and ourselves, Jesus brought the Father and ourselves together by what He accomplished in His own body, reconciling us through the blood of His Cross.
In the Bible,
“the life of the flesh is in the blood” (Leviticus 17:11).
The victim slain in sacrifice was not the vicarious recipient of a punishment, but the symbol of the loving dedication of the life of the person making the sacrifice.
This sacrificial dedication of life is the means by which the sinner is made “at one” with God.