There is no servant except that there exists a white spot upon his heart. So when he commits a sin, a black spot arises into that white spot. Then when he repents, this black spot moves away. But if he continues on committing sins, the blackness of this spot increases till such time that it overwhelms and overrides the whiteness. When the whiteness is all covered over (by the blackness), the owner of it (the heart) does never at all return towards beneficence and goodness. And This is what God means when he says: "Nay! rather, what they used to do has become like a rust upon their hearts."
I admonish you regarding five things:
Consider the world as an abode where in you have dropped down for an hour, then you have got to leave it and go ahead; or (suppose it is) like the wealth which you lay hands upon in a dream and become over-joyed and glad. Then you wake up to find yourself empty handed.