…Happiness and joy are not really the same, though they are clearly linked. In many ways, happiness is the world’s cheap imitation of joy, perhaps the way lust is a lesser substitution of romantic love. Happiness is temporal and physical; joy is eternal. Happiness is primarily a feeling; joy is primarily a choice. Happiness is easy, since it requires the absence of pain; joy is often quite difficult, coming in spite of pain. Happiness is self-centered; joy is others-centered and God-centered. Happiness is surface level; joy is soul level.
To set a marriage relationship—or any relationship—upon a foundation of happiness is to build on a most unsteady surface indeed. When the inevitable rains and floods come, the edifice is destined to collapse, likely crushing the people inside.