"The Zohar (Vayechi) has declared: 'The righteous have reason to rejoice on the day of their departing...' And it states (Ibid. Vayera): 'Death is the suffering of the body and the rejoicing of the soul,' for the soul of the saintly longs for the time when it will depart from this vain world and enjoy the world of bliss. At the time of parting the soul has joy. Hence the anniversary of the death of a Tzaddik is called Hilula (festivity)." Gaon