Even the rational intellect can recognize that the human mind is unable to directly cognize and assimilate the entirety of the manifested universe. As humanity pushes ever farther in its examination of the facts of existence, this principle becomes ever more clear. We now know that the range of perceptions we have is limited both on the top and the bottom end, while other beings have the ability to perceive within different ranges, including some which are hidden from us. Just as we can recognize the limitations of the senses and the sense experience, we also have begun to recognize that forces at work which cannot be directly perceived, necessarily, but which have specific visible effects. This recognition of invisible forces which can be harnessed to our needs has led to the development of the theories of gravitation, the electro-magnetic spectrum and wireless transmission of energy and content. The laws of physics regarding momentum and inertia, and eventually the atomic theory which has brought about the ability to convert matter into energy are examples of forces outside the direct cognizance of our senses which nevertheless can be seen to exist. Quantum mechanics goes further in describing existence in ways that our senses would, at first, tend to deny. Similarly, exploration into biological processes shows us how our knowledge of the physiology of life is lacking.
The limiting intelligence of the mind has a similar inability to recognize higher realms of consciousness that nevertheless not only must be at work for the creation to exist in the first place, but which can be experienced through other means than the intellect. It is here that the spiritual intuition comes in to validate the truths of our existence that the mind cannot, at this stage of its development, prove to exist.
Sri Aurobindo observes: Spiritual intuition is always a more luminous guide than the discriminating reason, and spiritual intuition addresses itself to us not only through the reason, but through the rest of our being as well, through the heart and life also. The integral knowledge will then be that which takes account of all and unifies their diverse truths. The intellect itself will be more deeply satisfied if it does not confine itself to its own data, but accepts truth of the heart and the life also and gives to them their absolute spiritual value.”
Sri Aurobindo, The Synthesis of Yoga, Part Three: The Yoga of Divine Love, Chapter 5, The Divine Personality, pg. 553