The human being is not purely a physical entity, nor even a vital-physical being. We recognise and understand that there is a mental component to human life that can be self-reflective and can separate itself from the physical and vital being and observe, understand and respond in ways other than purely for the fulfillment of physical needs or vital desires or drives.
The ancient sages of the Upanishads saw the human being as consisting of multiple different bodies, or sheathes, with their own different characteristics that had to interact with each other under the circumstances of the life in the body.
Sri Aurobindo describes the mental body and its relationship to the vital-physical being of man: “Man too has in himself, subliminal, unknown and unseen concealed behind his waking consciousness and visible organism this mental soul, mental nature, mental body and a mental plane, not materialised, in which the principle of Mind is at home and not as here at strife with a world which is alien to it, obstructive to its freedom and corruptive of its purity and clearness. All the higher faculties of man, his intellectual and psycho-mental being and powers, his higher emotional life awaken and increase in proportion as this mental plane in him presses upon him. For the more it manifests, the more it influences the physical parts, the more it enriches and elevates the corresponding mental plane of the embodied nature. At a certain pitch of its increasing sovereignty it can make man truly man and not merely a reasoning animal; for it gives then its characteristic force to the mental being within us which our humanity is in the inwardly governing but still too hampered essence of its psychological structure.”
Sri Aurobindo, The Synthesis of Yoga, Part Two: The Yoga of Integral Knowledge, Chapter 21, The Ladder of Self-Transcendence, pp. 451-452