God publicly set forth Christ Jesus as a propitiation—a sacrifice that satisfies God's wrath and turns away His righteous anger against sin—effective through His shed blood, to be appropriated through faith. God did this to demonstrate His own righteousness and justice, because in His patient forbearance during past ages, He had passed over sins previously committed without immediate full punishment.
This demonstration of righteousness continues at the present time, so that God might be shown to be both perfectly just in His own character and the one who justifies or declares righteous the person who places his faith in Jesus.