The Bowl of Saki Commentary

Now the true condition of the heart is this, that it carries nothing. It cannot contain two things, but the unity it holds in love may be simple or complex, very large or greater than the whole universe. This is the explanation of the teaching of the Upanishads. In the Upanishads, Atman often means the same as heart-essence, and this heart-essence grasps both great and small, but whatever it holds, it holds nothing else.

For that reason Sufis practice heart-concentration, first to restore to the heart its faculty of grasping and then to prepare the heart for grasping that which alone does it good; that is to say, to grasp God, to hold God. All Sufi practices have this object in view.