John gives us a sobering reminder that we cannot simultaneously live for the "things of the world" and live for God. Ultimately, we will give our lives to something—we will look for fulfillment in something. John shows us why it's foolish to look for joy in the things of the world: because they are passing away and were never designed to satisfy. We were Created by God and for God, and it is only in God that we will find what our hearts are longing for.