A generation ago, C. S. Lewis set out to write a book on love, using as his main text: "God is Love" from 1 John 4:

Beloved, let us love one another, because love is from God; everyone who loves is born of God and knows God. Whoever does not love does not know God, for God is love. God's love was revealed among us in this way: God sent his only Son into the world so that we might live through him. In this is love, not that we loved God but that he loved us and sent his Son to be the atoning sacrifice for our sins. -- 1 John 4:7-10

His plan, he later revealed, was a simple one. He would divide the various human emotions we tend to lump together as love into two categories: Need-love and Gift-love. Need-love, in Lewis' system, was fundamentally self-centered and self-serving, meeting our o…