The greatest power in the realm and range of human existence is spirit—the divine breath which animates and pervades all things. It is manifested throughout creation in different degrees or kingdoms. In the vegetable kingdom it is the augmentative spirit or power of growth, the animus of life and development in plants, trees and organisms of the floral world. In this degree of its manifestation spirit is unconscious of the powers which qualify the kingdom of the animal. The distinctive virtue or plus of the animal is sense perception; it sees, hears, smells, tastes and feels but is incapable, in turn, of conscious ideation or reflection which characterizes and differentiates the human kingdom. The animal neither exercises nor apprehends this distinctive human power and gift. From the visible it cannot draw conclusions regarding the invisible, whereas the human mind from visible and known premises attains knowledge of the unknown and invisible… The animal spirit cannot penetrate and discover the mysteries of things. It is a captive of the senses. No amount of teaching, for instance, would enable it to grasp the fact that the sun is stationary, and the earth moves around it. Likewise, the human spirit has its limitations. It cannot comprehend the phenomena of the Kingdom transcending the human station, for it is a captive of powers and life forces which have their operation upon its own plane of existence, and it cannot go beyond that boundary.
- ‘Abdu’l-Baha (From a talk, 25 April 1912, Washington, D.C.; ‘The Promulgation of Universal Peace: Talks Delivered by 'Abdu'l-Bahá during His Visit to the United States and Canada in 1912’)