"God displayed [Jesus Christ] publicly as a Mercy Seat through faith in His blood. This was to demonstrate His righteousness, because in the forbearance of God He passed over the sins previously committed;"
We have a public mercy seat for the forgiveness of sins, but not everyone realizes what it is. They see it clearly, but they do not understand it because it is not of this world, but now that this mercy seat has been revealed, there is no excuse not to come to it other than a failure to recognize it for what it is, that is a failure to recognize the goodness of the revealed Christ because it is foolishness to the wise and incomprehensibly foreign sinful man.
This is why we Christians must lead others to the mercy seat and testify to it's goodness. The grace is publicly available to all and is not resisted but simply not understood as grace. God's sovereign work is not recognized and is his basis for judgment because now that there is no condemnation in Christ, there is no justification for remaining condemned. The world must be brought to recognize Christ and confess that He is Lord and He is for them. They only need to come to the mercy seat empty-handed.
This is the good news that we take part in sharing: That God has elected himself for suffering and damnation and that God has elected us for salvation through Christ. Salvation has come to all men, so come to salvation!