The soul feels suffocated when the doors of the heart are closed.

Commentary by Hazrat Inayat Khan:

There is a door to man's heart; it is either closed or open. When he holds a thing and says, 'This is mine,' he closes the door to his heart; but when he shares his goods with others and says, 'This is yours as well as mine,' this opens his heart. We must learn consideration for others; it does not matter whether they are rich or poor. We may have only one slice of bread, but when there is another sitting by our side we share that slice with him. By doing this, even if our bodily appetite remains unsatisfied, our heart is filled with joy to think that we shared our happiness with another. It is this spirit which is necessary just now to change the condition of the world, not political and commercial disputes. We must be awakened to the main truth, that the happiness and peace of each can only be the happiness and peace of all.

People pursue spirituality with their brain: that is where they are mistaken. Spirituality is attained through the heart. What do I mean by the heart? Is it the nervous center in the midst of the breast, the small piece of flesh that doctors call the heart? No, the definition of the heart is that it is the depth of the mind, the mind being the surface of the heart. That in us which feels is the heart, that which thinks is the mind. It is the same thing which thinks and feels, but the direction is different: feeling comes from the depth, thought from the surface. ... The Sufis have therefore considered the development of the heart quality as a spiritual culture, and have called it the culture of the heart. It consists of the tuning of the heart.

Tuning means changing the pitch of the vibrations. Tuning the heart means changing the vibrations, bringing them to a certain pitch which is the natural one where you feel the joy and ecstasy of life, which enables you to give pleasure to others even by your presence because you are tuned. When an instrument is properly tuned you need not play music on it; just by striking it you will feel a great magnetism coming from it. If an instrument well-tuned can have that magnetism, how much greater should be the magnetism of hearts that are tuned. Rumi says, 'Whether you have loved a human being or whether you have loved God, if you have loved enough you will be brought in the end into the presence of the supreme Love itself'.