Only a few verses back, Paul reminded us of the change that Christ makes in a life. Old things are made new. Here we see the reason.
Where did the old go? Where did the new come from? The old, the sin, the black damning stain went to Christ. "He made Him who knew no sin to be sin on our behalf." The Lord Jesus Christ took our "old" upon Himself at Calvary.
What is this "new" that we become? And what is its source? The new, the brilliantly clean heart that is within us and the glorious robe that is upon us came from Christ - "that we might become the righteousness of God in Him."
Blessed imputation!! Merciful salvation!!
Oh sinner - flee to Jesus. Your filthy rags may be traded in for the robe of His righteousness.