“What is the mercy seat?”……The writer to the Hebrews talks about the arrangement of the tabernacle of the Old Testament. The tabernacle was the portable sanctuary used by the Israelites from the time of their wandering in the wilderness after the Exodus from Egypt to the building of the Temple in Jerusalem (see Exodus 25├ö├ç├┤27).

Within the tabernacle was the Ark of the Covenant which included the mercy seat

Hebrews 9:3-5Then there was a curtain, and behind the curtain was the second roomcalled the Most Holy Place.In that room were a gold incense altar and a wooden chest called the Ark of the Covenant, which was covered with gold on all sides. Inside the Ark were a gold jar containing manna, Aaron's staff that sprouted leaves, and the stone tablets of the covenant.Above the Ark were the cherubim of divine glory, whose wings stretched out over the Ark's cover, the place of atonement. But we cannot explain these things in detail now.……The Ark of the Covenant, the chest containing the two stone tablets inscribed with the Ten Commandments, was the most sacred object of the tabernacle and later in the Temple in Jerusalem, where it was placed in an inner area called the Holy of Holies. Also within the ark were the golden pot of manna, such as was provided by God in the wilderness wanderings

Exodus 16:4 Then the Lord said to Moses, "Look, I'm going to rain down food from heaven for you. Each day the people can go out and pick up as much food as they need for that day. I will test them in this to see whether or not they will follow my instructions.

and Aaron's almond rod

Numbers 17:1-13

Then the Lord said to Moses, "Tell the people of Israel to bring you twelve wooden staffs, one from each leader of Israel's ancestral tribes, and inscribe each leader's name on his staff. Inscribe Aaron's name on the staff of the tribe of Levi, for there must be one staff for the leader of each ancestral tribe.

Place these staffs in the Tabernacle in front of the Ark containing the tablets of the Covenant, where I meet with you. Buds will sprout on the staff belonging to the man I choose. Then I will finally put an end to the people's murmuring and complaining against you." So Moses gave the instructions to the people of Israel, and each of the twelve tribal leaders, including Aaron, brought Moses a staff. Moses placed the staffs in the Lord's presence in the Tabernacle of the Covenant.

When he went into the Tabernacle of the Covenant the next day, he found that Aaron's staff, representing the tribe of Levi, had sprouted, budded, blossomed, and produced ripe almonds!

When Moses brought all the staffs out from the Lord's presence, he showed them to the people. Each man claimed his own staff.And the Lord said to Moses: "Place Aaron's staff permanently before the Ark of the Covenant[d] to serve as a warning to rebels. This should put an end to their complaints against me and prevent any further deaths." So Moses did as the Lord commanded him.

Then the people of Israel said to Moses, "Look, we are doomed! We are dead! We are ruined!Everyone who even comes close to the Tabernacle of the Lord dies. Are we all doomed to die?"

On top of the ark was a lid called the mercy-seat on which rested the cloud or visible symbol of the divine presence. Here God was supposed to be seated, and from this place He was supposed to dispense mercy to man when the blood of the atonement was sprinkled there.……In a manner of speaking, the mercy-seat concealed the people of God from the ever-condemning judgment of the Law. Each year on the Day of Atonement, the high priest entered the Holy of Holies and sprinkled the blood of animals sacrificed for the atonement of the sins of God’s people.

This blood was sprinkled on the mercy-seat. The point conveyed by this imagery is that it is only through the offering of blood that the condemnation of the Law could be taken away and violations of God's laws covered.……In the New Testament, the Greek word for "mercy-seat" in Hebrews 9:5 is hilasterion, which means "that which makes expiation," or "propitiation." It carries the idea of the removal of sin.

The brazen altar of sacrifice is also called hilasterion (the propitiatory or mercy-seat) because of its association with the shedding of blood for sin.

Ezekiel 43:14From the gutter the altar rises 3 1├ö├╝├ñ2 feet to a lower ledge that surrounds the altar and is 21 inches wide. From the lower ledge the altar rises 7 feet to the upper ledge that is also 21 inches wide……What is the significance of this? In the New Testament, Christ Himself is designated as our "propitiation." Paul explains this in his letter to the Romans: "being justified freely by His grace through the redemption that is in Christ Jesus, whom God set forth as a propitiation by His blood, through faith, to demonstrate His righteousness, because in His forbearance God had passed over the sins that were previously committed"

Romans 3:24-25Yet God, with undeserved kindness(grace), declares that we are righteous. He did this through Christ Jesus when he freed us from the penalty for our sins. For God presented Jesus as the sacrifice for sin. People are made right with God when they believe that Jesus sacrificed his life, shedding (propitiate)his blood. This sacrifice shows that God was being fair when he held back and did not punish those who sinned in times past,.

What Paul is teaching here is that Jesus is the covering for sin, as shown by these Old Testament prophetic images. By means of His death, and our response to Christ through our faith in Him, all our past sins are covered. Later in Romans, Paul pinpoints precisely when this occurs:

Romans 6:3-4 "Or have you forgotten that when we were joined with Christ Jesus in baptism, we joined him in his death? For we died and were buried with Christ by baptism. And just as Christ was raised from the dead by the glorious power of the Father, now we also may live new lives.

…It is when we, upon the basis of penitent faith, are buried with Christ in baptism, that we are raised in "newness of life." By our obedience to the divine commands, we are made "free from sin."

Also, whenever believers sin, we may turn to Christ who continues to be the propitiation or covering for our sins

1 John 2:1, 4:10My dear children, I am writing this to you so that you will not sin. But if anyone does sin, we have an advocate who pleads our case before the Father. He is Jesus Christ, the one who is truly righteousThis is real love-not that we loved God, but that he loved us and sent his Son as a sacrifice to take away our sins.

This ties together the Old and New Testament concepts regarding the covering of sin as exemplified by the mercy-seat of God.