Why have you despised the word of the Lord, to do what is evil in his sight? You have struck down Uriah the Hittite with the sword and have taken his wife to be your wife and have killed him with the sword of the Ammonites. Now therefore the sword shall never depart from your house, because you have despised me and have taken the wife of Uriah the Hittite to be your wife. ’ … [Nevertheless] Nathan said to David, “The Lord also has put away your sin; you shall not die…” (2 Sam 12:9-13)
How can God simply excuse such heinous sin? How can God just “put it away”—sin like that… like the sin of someone who has done the worst kind of wrong to you… we don’t want God to excuse it; we want Him to punish it. Here, David had slept with another man’s wife and then had him killed to cover up the deed. How can God “put away” his sin and forgive him?
That’s the issue in Romans 3:25:
“…in his divine forbearance he had passed over former sins.”
How can God “pass over” sins and excuse the truly guilty?
Above, I gave the last part of Rom 3:25, now check out what comes right before that:
“God put forward [Jesus] as a propitiation by his blood, to be received by faith. This was to show God’s righteousness…” (Rom 3:25).
The answer to the above question is that God could only maintain His own “innocence” (i.e., His justice or righteousness) for His mercy and forgiveness of sin by decisively punishing all sin, once for all, on Jesus who voluntarily substituted Himself for the guilty.