God publicly displayed him [Jesus] at his death as the mercy seat accessible through faith.
Romans 3:25a NET
In Exodus 25:17-22, God instructed Moses to build a cover for the Ark of the Covenant. In Exodus, this was called the Atonement Cover or the Mercy Seat. But this cover was much more than just a fancy lid for the ark. It represented God’s throne (2 Sam. 6:2). When you entered the Holy of Holies and stood before the mercy seat, you were standing before God on his throne, a sacred and holy place.
This cover was also the place where atonement was made for the sins of the people. On the Day of Atonement (Lev. 16), the high priest would offer several sacrifices. For two of them, the sin offerings for himself and the people, he was to bring the blood of the sacrifice into the Holy of Holies along with some incense. The smoke of the incense would hide the cover from view. And he would sprinkle the blood on the cover–God’s throne. In this way, atonement was made, first for his own sins and then for the people’s sins.
The Mercy Seat and the Atoning Sacrifice
This cover is mentioned twice in the New Testament, here and in Hebrews 9:5, which refers to the lid over the ark. But here in Romans 3:25, the reference is to Jesus. The NIV says that God presented Jesus as a sacrifice of atonement, a reference to the action of the high priest sprinkling the blood of the atoning sacrifice on the atonement cover. The NET says that God publicly presented Jesus as the mercy seat, the place of atonement.
Both are valid interpretations, and Paul likely intended both readings. Jesus is the mercy seat, where all the fulness of God dwells in bodily form (Col. 2:9). And he is the atoning sacrifice offered on the mercy seat (Heb. 9:11-14).
What is most significant here is that God offered the atoning sacrifice on the mercy seat. In every other religion, humanity offers sacrifices, seeking to appease their god’s wrath. But here we see that God offers the atoning sacrifice on our behalf.
Our salvation is based, not on what we do, but on what God does for us. All we must do is accept it by faith.