Romans 7

As Paul speaks of his earlier commitment to the law of Moses, he suggests that he felt satisfaction In his obedience, but not spiritual. That many sinned within the law of Moses by still appearing to live the law.  He then explains -

"But now we are delivered from the law, that being dead wherein we were held; that we should serve in newness of spirit, and not in the oldness of the letter."  (Romans 7:6)

In my mind, he now sensed a new commitment to the gospel of Jesus Christ, as he continues to repent and strive to live His commandments.  It is the gospel that brings joy.