"And thou shalt put the mercy seat above upon the ark; and in the ark thou shalt put the testimony that I shall give thee. And there I will meet with thee, and I will commune with thee from above the mercy seat" (Exodus 25:21-22).
In the "holy of holies" of the tabernacle, God would meet with Israel's high priest once a year to commune with His people at a meeting place called the "mercy seat." The Hebrew word was derived from the word for "atonement," which in turn meant essentially a "covering" for the Ark of the Covenant. On the great day of atonement each year, the high priest was commanded to sprinkle the blood from the sin offerings on the mercy seat (Leviticus 16:14-15) to make an atonement for all the people.
This annual ceremony, of course, merely prefigures the full atonement which Christ would make one day when "by His own blood He entered in once into the holy place, having obtained eternal redemption for us" (Hebrews 9:12). Since this blood has been sprinkled once for all on the heavenly mercy seat, as it were, we are now "justified freely by His grace through the redemption that is in Christ Jesus: Whom God hath set forth to be a propitiation through faith in His blood, to declare His righteousness for the remission of sins that are past, through the forbearance of God" (Romans 3:24-25).
In this verse, the word "propitiation" is the Greek word for "mercy seat" (and is so translated in Hebrews 9:5). That is, Christ Himself, with His atoning blood, is our mercy seat, where we can meet with God. Thus, the golden, blood-stained mercy seat becomes the very throne of God Himself, where He meets with those who believe on Him for salvation. "Let us therefore come boldly unto the throne of grace, that we may obtain mercy, and find grace to help in time of need" (4:16). HMM