One sentence in the Gospel lectionary reading for today, from Luke 10:21-24, really jumped out at me: "... Jesus rejoiced in the Holy Spirit..."
It seems to me that far too often we focus on Jesus as a man of sorrows. Certainly, he was that. He bore our griefs, as Isaiah prophesied. But more than that, Jesus was and is a man of joy. I think, perhaps, that is one of the main things that attracted other people to Jesus, and still does.
Joy is part of the fruit of the Holy Spirit, as Paul says in Galatians 5:22. Joy is a gift from God. It cannot be manufactured by human beings.
Happiness is different from joy. It turns up generally where you would expect it to do so: when one gets the job one has been longing for, when one has a merry meeting with one's friends, when the person of your dreams says "yes" to your proposal, or when that longed-for child is born. Happiness is dependent upon happenings, circumstances. Joy is not.
Joy is not rooted in our outward circumstances. Rather, it is grounded in our relationship with God. That is why joy is compatible with pain and sorrow. Joy turns up where you might least expect it: on the cancer ward, in the unemployment office, or even at a graveside. By the power of this gift from God, we are enabled, as Jesus was, to endure the difficult circumstances of this life, because of the joy set before us. (Hebrews 12:2)
As C. S. Lewis once wrote, "Joy is the serious business of heaven." (Letters to Malcolm: Chiefly on Prayer, p. 93)