From David K. Naugle:

Concerning happiness:

The grand union of God, ourselves, and the whole cosmos in a sacred synthesis of rightly ordered love constitutes the deep meaning of happiness.

This from his book: Reordered Love, Reordered Lives, p. 23. I have only finished reading the first chapter, so I can't say too much about it. But so far it is quite good. David Naugle is professor of philosophy at Dallas Baptist University, and also wrote Worldview: the History of a Concept, which is an excellent book.