‘Abdu’l Baha taught that the limited human intellect can know of the existence of God but cannot comprehend the Divine essence.
‘Now concerning the Essence of Divinity: in truth it is on no account determined by anything apart from its own nature, and can in no wise be comprehended. For whatsoever can be conceived by man is a reality that hath limitations and is not unlimited; it is circumscribed, not all-embracing. It can be comprehended by man, and is controlled by him. Similarly it is certain that all human conceptions are contingent, not absolute; that they have a mental existence, not a material one. Moreover, differentiation of stages in the contingent world is an obstacle to understanding. How then can the contingent conceive the Reality of the absolute? As previously mentioned, differentiation of stages in the contingent plane is an obstacle to understanding. Minerals, plants and animals are bereft of the mental faculties of man that discover the realities of all things, but man himself comprehendeth all the stages beneath him. Every superior stage comprehendeth that which is inferior and discovereth the reality thereof, but the inferior one is unaware of that which is superior and cannot comprehend it. Thus man cannot grasp the Essence of Divinity, but can, by his reasoning power, by observation, by his intuitive faculties and the revealing power of his faith, believe in God, discover the bounties of His Grace. He becometh certain that though the Divine Essence is unseen of the eye, and the existence of the Deity is intangible, yet conclusive spiritual proofs assert the existence of that unseen Reality. The Divine Essence as it is in itself is however beyond all description’.