As Jesus’s beloved disciple John grew older, his teaching became increasingly narrowed, focusing entirely on the love of God in his three letters. In the book Knowing the Truth of God’s Love, Peter Kreeft cites an old legend which says that one of John’s young disciples once came to him complaining, “Why don’t you talk about anything else?” John replied, “Because there isn’t anything else.”

God’s love is certainly at the heart of the mission and message of Jesus. In his earlier gospel account, John recorded the words, “For God so loved the world that he gave his one and only Son,…