25 God presented Christ as a sacrifice of atonement, through the shedding of his blood-to be received by faith. He did this to demonstrate his righteousness, because in his forbearance he had left the sins committed beforehand unpunished-
25 Whom God hath set forth set forth: or, foreordained 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;
English Standard Version
25 whom God put forward as a propitiation by his blood, to be received by faith. This was to show God's righteousness, because in his divine forbearance he had passed over former sins.
25 God sacrificed Jesus on the altar of the world to clear that world of sin. Having faith in him sets us in the clear. God decided on this course of action in full view of the public - to set the world in the clear with himself through the sacrifice of Jesus, finally taking care of the sins he had so patiently endured.