What is a human being?

A human being is a microcosm of consciousness, the first level of expression capable of experiencing all things. Love gives it the desire to experience
the sense of separation, eventually forgetting its true nature of oneness, eventually leading to the desire to abandon the egoic self and return to the unitive state of consciousness. It is the first level of consciousness able to be aware that it is essentially pure without any attributes or divisions. Human beings can also realize the absolute beyond oneness. This is the end of all experience, and what we call noble wisdom, full awakening, or true enlightenment.
The human being is the manifestation that is the alpha and omega of awareness, from the alpha of pure awareness as the only aspect of oneness, to the omega of fully individuated consciousness with a personal heart/mind/body/spirit. The resolution of the alpha and omega and all between is the freedom from existence itself that realization of the absolute brings. There should be little doubt that the expression of consciousness does not end with the complex manifestation of human beings. As it is said by sages from ancient times to modern, there are continuing levels and dimensions beyond earth - Buddha realms, infinite worlds, and infinite varieties of beings. Yet we are able to realize the impermanent and illusory nature of it all.
My sources are many of the great texts and sutras, various modern teachings, dialogs, independent studies, decades of inquiry and observation into all areas of life, and ongoing silent mind and contemplative practice.