The mind is not an instrument of knowledge. It is an analytical and organising tool, but is unable, on its own, to establish truth or certainty. It also maintains a certain arrogance in its own powers, and thus, when confronted with something beyond its own capabilities, it doubts the veracity and asks for proof. Some things, however, cannot be proven to the satisfaction of the intellect; however, that does not disprove those things. The Kena Upanishad tells the tale of how the powers of the body, the life energy and the mind thought they were each powerful and masters of the existence of the earth. But at some point, their powers were nullified by something which they could not understand or define. The mental power exceeded itself and came to know that there was a greater power, the Eternal, which created and maintained all the lesser powers of the creation.
This does not imply that there cannot be some instrument of knowledge, but it is not contained within the powers of body, life and mind; rather, it is the psychic being, the soul, which is a spark of the Divine in the individual being, and thus, through its oneness, is able to know what these other powers cannot. The knowledge of the soul cannot be proven with the tools of the intellect, but are expressed through the inner certainty that we call faith.
Sri Aurobindo observes: “… faith in the spiritual sense is not a mental belief which can waver and change. It can wear that form in the mind, but that belief is not the faith itself, it is only its external form. Just as the body, the external form, can change but the spirit remains the same, so it is here. Faith is a certitude in the soul which does not depend on reasoning, on this or that mental idea, on circumstances, on this or that passing condition of the mind or the vital or the body. It may be hidden, eclipsed, may even seem to be quenched, but it reappears again after the storm or the eclipse; it is seen burning still in the soul when one has thought that it was extinguished for ever. The mind may be a shifting sea of doubts and yet that faith may be there within and, if so, it will keep even the doubt-racked mind in the way so that it goes on in spite of itself towards its destined goal. Faith is a spiritual certitude of the spiritual, the divine, the soul’s ideal, something that clings to that even when it is not fulfilled in life, even when the immediate facts or the persistent circumstances seem to deny it. This is a common experience in the life of the human being; if it were not so, man would be the plaything of a changing mind or a sport of circumstances.”
Sri Aurobindo and the Mother, Growing Within: The Psychology of Inner Development, Chapter III Growth of Consciousness Basic Requisites, pp. 42-43