Woodenly, it says, “to declare His righteousness on account of the passing-over of before-happened sins.” That still might mean “God had passed over sin, and therefore people thought Him unconcerned with sin; He finally has shown that He’s serious about sin by putting forth Jesus as an expiating sacrifice.”

Perhaps, but it might also be taken to mean something else: first, that the passing-over was itself righteous, that God demonstrated His righteousness in forbearing in the face of sin; and, second, that the fact that His forbearance was righteous all along is shown when Jesus is set forth as a hilsterion. Either way, we cannot know God’s righteousness without the cross. But the two interpretations of the passage give us quite distinct interpretations of what God was up to in the Old Testament: Was His forbearance unrighteous or righteous? Was it an act of mercy that had to be “corrected” by the cross, or an act of justice whose justice is only evident after the cross?

via Peter J. Leithart » Blog Archive » Righteousness and sin.