The Baal Shem Tov thought of the Jew's relationship to God as a romance, and it disturbed him to see how many rituals had become routine rather than rapturous acts, exercises in repetition rather than gestures of surprise -- a hand without a heart. Faith was fire, not sediment. Did not a pillar of fire serve as a guide when the people Israel roamed in the wilderness? And fire was the beginning of light.
One of his contributions was to awaken a zest for spiritual living, expressed in hitlahavut, which literally means "being aflame" -- the experience of moments during which the soul is ablaze with an insatiate craving for God, when the memory of all other interests and the fear of misery and persecution are forgotten...The Baal Shem thought that obedience without passion, comformity without spontaneity was but a skeleton, dry, meager, lifeless. A Jew should serve God with ardor. It was necessary, vital, to have fire in the soul.
--from A Passion for Truth