Once when Bhagavan was asked what his central teaching was, he replied that the Centre itself was his central teaching. By the Centre he meant the Heart, the Source of everythingThough we do find mention about the Heart in the traditional scriptures, one does not find any satisfactory mention of it anywhere. Many take it as the physical heart. Though life and death are due to its throbbing and stopping, it is not the Spiritual Heart. Then, what is the Spiritual Heart? It is the source of consciousness felt as "I-I" in the Heart and also the source of thoughts. Hence Bhagavan directs us to watch the source from which the I-thought emanates.
The "I-thought disappears as one searches for its source. This is self enquiry."
Teaching based on Ramana's experience
Bhagavan has from his own experience revealed to us the location also of that Heart Centre. It is on the right side of the chest and not on the left. One may emphasize that it is the centre from which the mind with its root-thought "I" is born and it is the source of light and life in the individual. It is the natural centre where everyone feels his identity. The mind withdraws into it during sleep without knowing it. If one is consciously in touch with it seeking the source of one's being; then one transcends individuality.
Withdrawing consciously into it one experiences the Unity of the Self, in which all differentiation is lost and everything is experienced as nothing but the Self. That is blessedness and that is not only the summit of spiritual experience, but should be the quiet normal state of every being, the Reality of all beings. All suffering born of a false sense of separate individuality completely disappears and that is the state of unalloyed, perennial Bliss.
This merging in the Heart, the re-union with the ground of Being-Awareness, is what is working towards the ultimate goal. That is why earnest seekers, whatever their religion find Bhagavan's teaching not only acceptable but the very essence of their own tradition. What makes the teaching most attractive is that it is so clear, precise and definite and comes from a realized Sage. Also it carries with it a sense of special urgency because it is accompanied by the safe and simple method of self-enquiry, which is the practical and most useful side of Bahaman’s teaching. This method is explained in Who am I? Upadesa Sara and Forty Verses on Reality.