It was to show his righteousness at the present time, so that he might be just and the justifier of the one who has faith in Jesus. (ESV)
One of my favorite preachers, Chuck Swindoll, tells a story in his book, The Grace Awakening, of a father and a son. The son had done something disobedient. The father leads his son into the bedroom, and takes off his belt for an inevitable spanking. The child knows he is guilty. He kneels down at the bed and prepares for what he knows is coming.
Then something unexpected happens. The father tells the son to stand up. He hands the belt to his son and asks the son to strike his father with the belt instead. The child knows that the father did nothing wrong and resists, but finally, tearfully, obeys his father and gives the undeserved punishment. This was a lesson neither would forget.
Consider the situation of sinful mankind. We were like the guilty child in the above story. We rebelled against all of God's righteous commands. We did so willingly. We know that we are deserving of God's punishment. What does God do? He steps into the picture in the form of his son, Jesus. Jesus takes our punishment on his body for our sin.
Why did he do this? Paul tells us in our verse today. God did this to show his righteousness. He is able to be just (punishing sin), and yet he is able to justify unworthy sinners, declaring them righteous based on Christ paying for their sins, and their faith being placed in that gracious act. We serve a wonderful Savior.
God is just. He is also full of grace. Place your faith in the finished work of Jesus Christ on your behalf.