4 He is, however, above [all] these properties, and therefore indescribable. For He may well and properly be called an Understanding which comprehends all things, but He is not [on that account] like the understanding of men; and He may most properly be termed Light, but He is nothing like that light with which we are acquainted. And so, in all other particulars, the Father of all is in no degree similar to human weakness. He is spoken of in these terms according to the love [we bear Him]; but in point of greatness, our thoughts regarding Him transcend these expressions. If then, even in the case of human beings, understanding itself does not arise from emission, nor is that intelligence which produces other things separated from the living man, while its motions and affections come into manifestation, much more will the mind of God, who is all understanding, never by any means be separated from Himself; nor can anything [in His case] be produced as if by a different Being.
Source: Adversus haereses (New Advent)