So far, John has focused the first part of his letter on the concept of God as Light. Now, he begins the shift into the second major section of his letter by focusing on God as Love. He does so by using the art of contrast. Love vs. hate. Cain vs. Christ. At the end of the day, the point is clear: no love = no life. Love for one another is a critical mark of the believer. As those who have been loved extravagantly, we in turn love our brothers and sisters in Christ sacrificially and generously. This kind of love serves as assurance that our faith is genuine and very much alive.