Remember, in John's Gospel, in the discourse in the Upper Room, the night of our Savior's betrayal and the Last Supper, he spoke of his returning to the Father but of his sending another 'advocate' or 'paraclete' to take his place, that is, the Holy Spirit. Clearly then, both Jesus and the Holy Spirit have this office of pleading for, of taking the side of, and of arguing the case for the people of God. And this work of pleading our case the rest of the NT agrees is the joint work of both the Lord Christ and the Holy Spirit. Here John says we have Jesus Christ as our paraclete, our advocate, the one who pleads our case with God the Father . Hilasmos' is such a word and such a controversy.
Propitiation means the turning away of wrath, the placating of anger.
And that is, in fact, as careful research has demonstrated time and again, exactly what 'hilasmos' means. But the idea that God is a God of wrath, that he is angry with the wicked, and that that anger must be turned away from us if we are to be saved, is not a popular idea among sinners, including scholarly sinners, and a number of sophisticated efforts have been made to take the 'wrath' out of the word 'hilasmos'. Usually the claim is that the word means simply forgiveness or expiation. These writers point to the pagan religions, which all had the idea that their gods often lost their tempers, flew off the handle against their human subjects, and had to be appeased and mollified by gifts and presents. Remember in Homer's The Iliad that when the Greek expeditionary force set off to rescue Princess Helen, who had been captured and carried off to Troy, their ships were hampered by contrary winds.