People who think a lot about themselves and their plans for wealth and success—e.g., writing a bestselling book and being mentioned in the same sentence with Hemingway—tend to be unhappy. However, people who think a lot about Christ and His grace, the great doctrines of the faith, and how to love and serve others tend to be happy people.
At age 22, as a very young senior pastor of one of the first-ever mega-churches, Spurgeon and his church underwent a terrible tragedy. Throughout his life he struggled with depression. To counteract that depression, he preached much on happiness and was very quick to laugh.
No one has greater credibility to speak on this subject than Joni Eareckson Tada, who in July will mark the 50th anniversary of the accident that left her a quadriplegic.
Barry Corey has written an important book, Love Kindness: Discover the Power of a Forgotten Christian Virtue, which I thoroughly enjoyed. He advocates true kindness without reducing it to mere cosmetic niceness.