What is common between joy and sorrow?
My answer: Joy comes from God; sorrow leads to God. Through the Cross, sorrow is transformed into joy.
Simone Weil, in Waiting for God, says that the source is the same. She likens it to two sentences written on a wall in different colors. For one who cannot read, only the difference in color is noticed, not the words, not the message. For one who can read, the words and message are the same.
Weil does not say what the message is, but I suspect—no, I know—the message is, “God loves me.”