Strong’s Greek & Hebrew Dictionary = an expiatory (place or thing), i.e. (concretely) an atoning victim, or (special) the lid of the Ark (in the Temple) :- mercy seat, propitiation
Strong’s Greek & Hebrew Dictionary = atonement, i.e. (concretely) an expiator :- propitiation
Merriam-Webster = 1. The act of appeasing wrath and conciliating the favor of an offended person; the act of making propitious.
2. In theology, the atonement or atoning sacrifice offered to God to assuage his wrath and render him propitious to sinners. Christ is the propitiation for the sins of men.
The King James Version (AV) uses the word propitiation only 3 times. Paul uses it once and John uses it twice in his epistles. The word propitiation and atonement have close links, (See Dr. Jack’s Word Study on Atonement.) as well as the word expiation not used in AV text but used by theologians to explain reconciliation, which also has close ties. (See Dr. Jack’s Word Study on reconciliation.)
The word has its pictures in the Old Testament. For all have sinned, and come short of the glory of God; Being 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 3:23-25 KJV) The picture here is of the mercy seat of the Ark of the Covenant. The mercy seat was the lid on top. Once a year the high priest went into the Holy of Holies and sprinkled the blood of a bull for the remission of sins of the people of Israel. God showed them mercy after His faithful people followed this ritual requirement.
The Septuagint or the Greek translation of the Old Testament uses this word as in Exodus 25:17 And thou shalt make a mercy seat of pure gold.
Paul reminded the people that all have sinned. They have come up short of God’s standard of truth. To provide a way out of the dilemma of not being able to live up to God’s standard and therefore deserving the punishment due the crime, God had to show a way through His mercy. God sent Jesus to be that mercy seat for us. He revealed to us that He was the mercy seat. By his shed blood sprinkled on the mercy seat He appeased or averted God’s wrath and justice. He was the blood sacrifice that made Him the propitiation of our sins.
It was God who took the initiative to reconcile man to Himself. It is man’s part to respond to God’s call to restoration of lost fellowship with Him through propitiation received by faith in the blood sprinkled by Jesus.
John furthers extends the call to the whole world. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous: And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world. (1 John 2:1-2 KJV) Jesus is our advocate. He is the propitiation for our sins. He is the sacrifice on the cross that removed the separation between God and man. He became our substitute and assumed our obligations, removed our guilt, covered it, by the vicarious punishment, which He endured.
God did this because of His mercy, grace, and love. Herein is love, not that we loved God, but that he loved us, and sent his Son to be the propitiation for our sin. (1 John 4:10 KJV) God looked down at mankind floundering in sin and despair and sent His Son to be the meeting place between God and man. He provided a way to restoration with Himself through faith in the finished work of Jesus as the propitiation—making God propitious or showing His favor toward man. Jesus took the wrath of God upon Himself so that we might live in the grace and favor of God.
Jesus is our mercy seat. This is a work of grace. We can’t earn it or merit it. We receive it by grace through faith. God has shown us His mercy through Jesus.