'Propitiation' in the Bible
Whom God put forward [ before the eyes of all] as a mercy seat and propitiation by His blood [the cleansing and life-giving sacrifice of atonement and reconciliation, to be received] through faith. This was to show God's righteousness, because in His divine forbearance He had passed over and ignored former sins without punishment.
So it is evident that it was essential that He be made like His brethren in every respect, in order that He might become a merciful (sympathetic) and faithful High Priest in the things related to God, to make atonement and propitiation for the people's sins.
And He [ that same Jesus Himself] is the propitiation (the atoning sacrifice) for our sins, and not for ours alone but also for [the sins of] the whole world.
In this is love: not that we loved God, but that He loved us and sent His Son to be the propitiation (the atoning sacrifice) for our sins.