"It is a positive commandment to be happy during the festivals," Torah says. In Judaism the highest service to God is given through joy and happiness, praise and thanks. All sadness and suffering comes from a lack of appreciation of the great gifts we have been given and are being given daily. The festivals turn this around. We are constantly made aware of all the gifts of life, surrounded by friends, family, loved ones, delicious food, beautiful clothes, and joy. To fulfill the mitzvah of being happy on the holiday we eat wonderful meals, drink wine, wear festive clothing, and experience delight. A man is obligated to make his wife happy with lovely clothes (and in other ways), and to give sweets to his household. The happiness that a person has in doing a mitzvah is considered a service to God. This happiness itself is a healing from sorrow. Ultimately the festivals turn sorrow into joy.

Brenda Shoshanna in Jewish Dharma