Paul has gotten mostly past his unpleasantness, now he brings some of his Jewish scholarship back to the letter. It’s a great contrast: how the glory of Moses (the human symbol of the law) was apt to fade, but not life in the Spirit. It’s the different between Life and death. This must have been especially personal to Paul, since the first part of his life was dedicated to that very law that he now claimed could never bring life. This doesn’t mean we should throw out the Old Testament, but we should see the fulfillment that came through Jesus when we read the whole story.