Answer [by 'Abdu'l-Baha]: This is a usage of the people of the East; it is of Islam. Their purpose is that in every matter the commencement should be in the Name of God (i.e., everything we do must begin with the Name of God). As to its observance in the divine tablets, the purport is this: The reality of the Divine Entity is holy above comprehension, beyond definition, and far from the reach of imagination, for that which is imagined is finite, of man, and thereto man is infinite; and certainly the infinite is greater than the finite. Therefore, it is made evident that what is imagined is a creation and not the Creator, for the Essence of Divinity is beyond human imagination.
Now all people worship an imagination, for they have created a God in the realm of imagination and him they worship. If you ask a soul, when he is praying, who art thou worshiping? He will say, God. Which God? The God of my conception. When, in truth, what he imagines is not God. Hence, all people are worshippers of imaginations and ideals. Consequently, there is no pathway or escape for man except the Holy Manifestations, for, as we said the Essence of Divinity is pure, is holy and cannot be brought into the world of ideas. That which can be brought to ideation are the Holy and Divine Manifestations. Further than this, man has no other point for concentration. If he exceed that bound, it will be an imagination.
Therefore, the purpose of the word "He is God" is this: That visible Majesty (the prophet) is the Promised Beauty of the Sun of Reality, the Manifestation of the mysteries of Divinity and Deity, the Revealer of the mysteries of the Merciful, the Origin of the signs of singleness. And I begin with His Blessed Name. (‘Abdu’l-Baha, excerpts from a table talk in Akka in 1907, notes taken by Corine True; ‘Notes Taken at Acca’, booklet published by Baha’i Publishing Society, Chicago 1907)
Thou hast asked regarding the phrase, "He is God!" written above the Tablets. By this word it is intended that no one hath any access to the Invisible Essence. The way is barred and the road is impassable. In this world all men must turn their faces toward "Him-whom God-shall-Manifest." He is the "Dawning-place of Divinity" and the "Manifestation of Deity." He is the "Ultimate Goal," the "Adored One" of all and the "Worshipped One" of all. Otherwise, whatever flashes through the mind is not that Essence of essences and the Reality of realities; nay, rather it is pure imagination woven by man and is surrounded, not the surrounding. Consequently, it returns finally to the realm and conjectures. (‘Abdu'l-Baha, Tablets of ‘Abdu'l-Baha vol. 3)