From the essay Know Thyself by Rene Guenon:
We see that real knowledge is not based on the path of reason, but on the spirit and the whole being for it is none other than the realization of this being in all its states, which is the culmination of knowledge and the attainment of supreme wisdom. In reality, what belongs to the soul , and even to the spirit, represents only degrees on the path toward the intimate essence that is the true self; this self can be found only when the being has reached its own center, all its powers being united and concentrated as in a single point [the "I"] in which all things appear to it [i.e., as representations], since they are contained in this point as in their first and unique principle; thus the being is able to know everything as in itself and of itself, as the totality of existence in the oneness of its own essence.
When man knows himself in his deepest essence, that is, in the center of his being, then at the same time he knows his Lord. And knowing his Lord, he at the same time knows all things, which come from Him and return to Him. He knows all things in the supreme oneness of the Divine Principle, outside of which … ‘there is absolutely nothing which exists,’ for nothing can be outside of the Infinite. [that is, there is no "thing" that opposes itself to me]