I John 2:2 declares ‘And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world’ (KJV). There’s just one problem with this translation: ἱλασμός doesn’t mean ‘propitiation’, it means ‘expiation’.
When you ‘propitiate’ a deity you do the same thing as the natives do when they trundle up a volcano and toss a virgin in it to stop the angry god from destroying you and your fellow islanders.
When ‘expiation’ occurs you do the same thing as the Israelites did when they put their hands on the scapegoat and sent it off into the wilderness. That goat ‘bears your sins away’ where they can’t harm you anymore and their effects are ameliorated.
This is why accurate translation matters. The difference between rendering ἱλασμός propitiation and expiation is the difference between pagan ritual and revelation. The God of the Bible is the God who, in Christ, carries our sins off. That’s why he is our ἱλασμός. And he is our ἱλασμός because that is what he does.