The Zohar states that "When the tzaddik departs, he is to be found in all worlds, more than during his lifetime." Now this needs to be understood. For, granted that he is to be found increasingly in the supernal worlds, because he ascends to there; but how is he found more in this world? As is known, the life of a tzaddik is not a physical life but a spiritual life, consisting wholly of faith, awe, and love of G-d... While the tzaddik was alive on earth, these three attributes were contained in their physical vessel and garment on the plane of physical space... his disciples received but a reflection of these attributes, a ray radiating beyond this vessel by means of his holy utterances and thoughts... But after his passing... whoever is close to him can receive a [far loftier dimension] of these three attributes, since they are no longer confined within a [material] vessel, nor bounded by physical space. -- Rabbi Schneur Zalman (Tanya, Iggeret HaKodesh 27)