What did Jesus do on the cross?
He was One whom God set up as a mercy seat—the place of atonement:
Romans 3:21-27 … and the righteousness of God [is] through the faith of Jesus Christ to all, and upon all those believing—for there is no difference, for have sinned and fallen short of the glory of God—being declared righteous freely by His grace through the redemption that [is] in Christ Jesus, whom God set forth as a mercy seat, through the faith in his blood, to show His righteousness, because of His forbearance of past sins—to show His righteousness in the present time, for His being righteous, and declaring that those who have faith in Jesus are righteous. (based on Young’s Literal Translation)
So what is this mercy seat? It was the cover of the Ark:
Exodus 25:17,22 “Then make the Ark’s cover—the place of atonement—from pure gold. … 22 I will meet with you there and talk to you from above the atonement cover between the gold cherubim that hover over the Ark of the Covenant. From there I will give you my commands for the people of Israel.
Before we go further, Paul’s audience was Jewish, so they would have known this any far richer ways than we modern Gentiles ever could.
Back to the mercy seat, God’s presence was always there:
Leviticus 16:2For the Ark’s cover—the place of atonement—is there, and I myself am present in the cloud above the atonement cover.
It was where God spoke with Moses:
Numbers 7:89 Whenever Moses went into the Tabernacle to speak with the Lord, he heard the voice speaking to him from between the two cherubim above the Ark’s cover—the place of atonement—that rests on the Ark of the Covenant. The Lord spoke to him from there.
Jesus is the place of our atonement. He is where we are purified. He is the place where we can meet with God. He is also the means of atonement.
Jesus is the mercy seat. The mercy seat was where, on the Day of Atonement, the High Priest would sprinkle a small amount of blood to:
Leviticus 16:16 … purify the Most Holy Place … because of the defiling sin and rebellion of the Israelites.
It was His blood that was offered for our sins, and he took all our sins and the consequences—the suffering, the pain and sorrow—on Himself.
2 Corinthians 5:21 For God made Christ, who never sinned, [to be the offering for our sin/be made sin], so that we could be made right with God through Christ.
Through faith in Jesus’ blood (a ludicrous thing to the sophisticated western mind), we can receive God’s righteousness. Some think of this received righteousness as an event, others as the start and basis of a lifelong process; nevertheless, it is something every believer can receive by faith.
Read more: A Biblical View of Christ’s Death