Lewis addresses what he designates as the four loves--Affection, Friendship, Eros, and Charity--within the context of the two main types of love--Need-love and Gift-love. He explains both the natural and supernatural aspects found in each (though Charity is only a result of the supernatural--Christ working in us). While much could be said about this book, I will just include my favorite quotation from it:
". . . as a better writer has said, our imitation of God in this life--that is, our willed imitation as distinct from any of the likenesses which He has impressed upon our natures or states--must be an imitation of God incarnate: our model is the Jesus, not only of Calvary, but also of the workshop, the roads, the crowds, the clamorous demands and surly oppositions, the lack of all peace and privacy, the interruptions. For this, so strangely unlike anything we can attribute to the Divine life in itself, is apparently not only like, but is, the Divine life operating under human conditions" (6).
If you're looking for a good intellectual, inspiring read, this may be the book for you! :D