If a tablet is not wiped clean of it's figures, nothing can be written upon it. A single heart cannot serve as the place for two things, let alone for several things. If the heart is filled with the forms of sensory perceptions, it is rare that it would perceive the meaning of Allah, even if one were to say Allah a thousand times. When the heart is empty of all that is other-than-God, if one uttered Allah only once, one would find such bliss that the tongue could not describe.
Source: The Key To Salvation: A Sufi Manual of Invocation, 1996. p. 92-93
Contributed by: Zaady