propitiation
Literally, a propitiatory sacrifice, through faith by his blood; (Greek, "hilastērion", "place of propitiation"). The word occurs, (1 John 2:2); (1 John 4:10) as the translation of the Greek, "hilasmos", "that which propitiates," "a propitiatory sacrifice." "Hilasterion" is used by the Septuagint, and (Hebrews 9:5) for "mercy-seat." The mercy-seat was sprinkled with atoning blood in the day of atonement (Leviticus 16:14) in token that the righteous sentence of the law had been (typically) carried out, so that what must else have been a judgment-seat could righteously be a mercy-seat; (Hebrews 9:11-15); (Hebrews 4:14-16); a place of communion (Exodus 25:21); (Exodus 25:22).
In fulfilment of the type, Christ is Himself the "hilasmos", "that which propitiates," and the "hilasterion", "the place of propitiation" -- the mercy-seat sprinkled with His own blood -- the token that in our stead He so honoured the law by enduring its righteous sentence that God, who ever foresaw the cross, is vindicated in having "passed over" sins from Adam to Moses (Romans 5:13) and the sins of believers under the old covenant
( See Scofield) - (Exodus 29:33)
and just in justifying sinners under the covenant. There is no thought in propitiation of placating a vengeful God, but of doing right by His holy law and so making it possible for Him righteously to show mercy.
remission
Passing over of sins done aforetime, that is, since Adam.
Compare (Hebrews 9:15).