For the naturalist (such as Ayn Rand), joy is peripheral while sorrow is central. This is because the superficial questions of life are answered but the fundamental questions are unanswered.
For the Christian (C.S. Lewis), sorrow is peripheral and joy is central. Superficial questions are unanswered, but the fundamental questions of life are answered.
(from G.K. Chesterton)
That is the essence.