The central truth of the Upanishads, the essence of the Vedanta, the goal of all wisdom and all spiritual practices, the reality of all realities, the quintessence of truth is that the individual self, the embodied soul, the Jiva, is identical with the Supreme, the Absolute, the Brahman, and this is what is meant by the great utterance of Self-revelation of the Upanishads: 'Tat Tvam Asi', That thou art. The nature of the inner essence of yourself and the nature of Brahman is one and the same, free from all change, impersonal and all-pervasive, infinite consciousness.
The heart is the source of our entire being. All our different faculties are like different rays branching out from the central light of the heart which is like the Sun. All our energies are conduits of the energy of the heart, however far they may wander from it. In deep sleep we return to this inner light for peace and renewal, showing that we cannot remain apart from it even for a day.