Since every other thought can occur only after the rise of the 'I'-thought and since the mind is nothing but a bundle of thoughts, it is only through the inquiry 'Who am I?' that the mind subsides. Moreover, the integral 'I'-thought, implicit in such enquiry, having destroyed all other thoughts, gets itself destroyed or consumed, just as the stick used for stirring the burning funeral pyre gets consumed.Tulku Urgyen Rinpoche says:
Even when extraneous thoughts sprout up during such enquiry, do not seek to complete the rising thought, but instead, deeply enquire within, 'To who has this thought occurred?' No matter how many thoughts thus occur to you, if you would with acute vigilance enquire immediately as and when each individual thought arises to whom it has occurred, you would find it is to 'me'. If then you enquire 'Who am I?' the mind gets introverted and the rising thought also subsides. In this manner as you persevere more and more in the practice of Self-enquiry, the mind acquires increasing strength and power to abide in its Source.
Repeatedly you hear, 'recognize mind essence; attain stability in that'. What this really means is that we should repeatedly look into what thinks. We should recognize the absence or emptiness of this thinker over and over again, until finally the power of deluded thinking weakens, until it is totally gone without a trace. At that point, what remains to prevent the state of enlightenment?
In the recognition of mind nature, the thought has no power to stand on its own. It simply vanishes. Just as our nature is emptiness, so is the nature of the thought. The moment of recognizing the thinker as empty cognizance is like the snowflake meeting the water.
It is only when the subtle mind is externalized through the activity of the intellect and the sense-organs that gross name and form constituting the world appear. When, on the other hand, the mind stays firmly in the Heart, they recede and disappear.Tulku Urgyen Rinpoche:
Samsara is mind turned outwardly, lost in its projections;
Nirvana is mind turned inwardly, recognizing its true nature.