Here is what you submitted in Post #52 when you first defined the word "propitiation hilasmos" :
quote=brightfame52
That word propitiation hilasmos:
a propitiation (of an angry god), atoning sacrifice. hilasmós – properly, propitiation; an offering to appease (satisfy) an angry, offended party. Christ's atoning blood that appeases God's wrath,
end quote
and here in red and blue is what you neglected to include in your definition of hilasmos:
2434 hilasmós – properly, propitiation; an offering to appease(satisfy) an angry, offended party. 2434 (hilasmós) is only used twice (1 Jn 2:2, 4:10) – both times of Christ's atoning blood that appeases God's wrath, on all confessed sin. By the sacrifice of Himself, Jesus Christ provided the ultimate 2434 /hilasmós("propitiation").
What you left out (in red and blue) answers your question "what exactly propitiates God ?"
Information from International Standard Bible Encyclopedia - Propitiation:
...
hilasmos, is found in the New Testament only in 1 Jn 2:2; 4:10. Here the idea is active grace, or mercy, or friendliness. The teaching corresponds exactly with that in Romans. "Jesus Christ the righteous" is our "Advocate (margin "Helper") with the Father," because He is active mercy concerning (peri) our sins and those of the whole world.
...
It is especially to be noted that all provisions for this friendly relation as between God and offending man find their initiation and provision in God and are under His direction, but involve the active response of man. All heathen and unworthy conceptions are removed from the Christian notion of propitiation by the fact that God Himself proposed, or "set forth," Christ as the "mercy-seat," and that this is the supreme expression of ultimate love. God had all the while been merciful, friendly, "passing over" man's sins with no apparently adequate, or just, ground for doing so. Now in the blood of Christ sin is condemned and expiated, and God is able to establish and maintain His character for righteousness, while He continues and extends His dealing in gracious love with sinners who exercise faith in Jesus. The propitiation originates with God, not to appease Himself, but to justify Himself in His uniform kindness to men deserving harshness.
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And, again, from Vines Expository Dictionary:
Propitiation:
[ B-2,Noun,G2434, hilasmos ]
akin to hileos ("merciful, propitious"), signifies "an expiation, a means whereby sin is covered and remitted." It is used in the NT of Christ Himself as "the propitiation," in 1Jo 2:2; 4:10, signifying that He Himself, through the expiatory sacrifice of His Death, is the Personal means by whom God shows mercy to the sinner who believes on Christ as the One thus provided. In the former passage He is described as "the propitiation for our sins; and not for ours only, but also for the whole world." The italicized addition in the AV, "the sins of," gives a wrong interpretation. What is indicated is that provision is made for the whole world, so that no one is, by Divine predetermination, excluded from the scope of God's mercy; the efficacy of the "propitiation," however, is made actual for those who believe. In 1Jo 4:10, the fact that God "sent His Son to be the propitiation for our sins," is shown to be the great expression of God's love toward man, and the reason why Christians should love one another.