Joy is not happiness. The difference between the two is not altogether different from love and lust. One is enthroned within the spirit and unwavering, the other fleeting and confined to circumstance.
There is a common assumption about those who have joy. Namely, that such individuals don’t have bad days (in the sense that bad circumstances do not happen to them). I have people assume this about me constantly. No, we all have our own share of darkness we must face. Even in the midst of such black winds, joy stands firm, unblinking. Our tears are never salty when tempered by joy.
Joy is a perspective, a faith, a hope. It stains the eye with eternal sunlight. Even when the sun is shrouded by clouds, it knows that it still shines. It is rooted in the trust that God has prevailed and nothing in this world can stand before Him. Trust in His love for us and faith in His the hope it brings gives us a levity in our hearts. Death does not frighten us; we laugh at darkness, even in the cloth of night.
More than that, it is a trust that He wants, and has, good for us. That the bitter may become sweet. It is a recognition of the beauty He has made in all things.
Perhaps more than anything else it is a thankfulness for each moment, realizing the divine hand by which we have been given them. Thankfulness for what we have, we have had, and what is yet to come. Thankful that even in suffering it is only temporary, and in it we may find more joy. Those who have known the most heartache also know the most love; the most pain, the most comfort; the supreme dark, supreme light.
In the perspective of eternity, the terrible fades away, the good shines forever. And thus we may smile in the rain, our hearts untouched by the torrent.