Desiring God by John Piper
The pursuit of true virtue includes the pursuit of the joy because joy is an essential component of true virtue. This is vastly different from saying, “Let’s all be good because it will make us happy. The reason this may sound strange is that we are more accustomed to think about our duty than God’s design. And when we do ask about God’s design, we are too prone to describe it with ourselves at the center of God’s affections. We may say, for example, that His design is to redeem the world. If God were not infinitely devoted to the preservation, display, and enjoyment of His own glory, we could have no hope of finding happiness in Him.