Propitiation literally means "appeasement" or "satisfaction."
In theological terms, it means that God's Wrath against sin, (demanded by His Justice), is appeased, or satisfied, on account of the Death of the Lord Jesus Christ for sinners.
Let the reader note here, that sin must be dealt with - God's Justice demands it. We cannot have this sin dealt with through our own means. Good conduct does not wipe out past sins.
It is only through the substitutionary Death (ie in place of the sinner) of the Lord Jesus Christ that the wrath of God against a man or woman can be satisfied or appeased.
So, then , the unsaved person must ask themselves - do I want to bear the Wrath of God for my sin eternally, or will I repent and receive the Lord Jesus Christ as my Saviour, and have this condemnation removed from against my name and person ?
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Romans 3: 23-26
"23 For all have sinned, and come short of the Glory of God;
24 Being justified freely by His Grace through the Redemption that is in Christ Jesus:
25 Whom God hath set forth to be a Propitiation through faith in His Blood, to declare His Righteousness for the remission of sins that are past, through the forbearance of God;
26 To declare, I say, at this time His Righteousness: that He might be just, and the justifier of him which believeth in Jesus.”
"... he is a rewarder of them that diligently seek him" Hebrews 11:6