Philo Judaeus De Mutatione Nominum 7

Do not, however, think that the living God, he who is truly living, is ever seen so as to be comprehended by any human being; for we have no power in ourselves to see any thing, by which we may be able to conceive any adequate notion of him; we have no external sense suited to that purpose (for he is not an object which can be discerned by the outward sense), nor any strength adequate to it: therefore, Moses, the spectator of the invisible nature, the man who really saw God (for the sacred scriptures say that he entered "into the darkness," ¹ by which expression they mean figuratively to intimate the invisible essence), having investigated every part of every thing, sought to see clearly the much-desired and only God;