Since Celsus, moreover, from a desire to depreciate the accounts which our Scriptures give of the kingdom of God, has quoted none of them, as if they were unworthy of being recorded by him (or perhaps because he was unacquainted with them), while, on the other hand, he quotes the sayings of Plato, both from his Epistles and the Phædrus, as if these were divinely inspired, but our Scriptures were not, let us set forth a few points, for the sake of comparison with these plausible declarations of Plato, which did not however, dispose the philosopher to worship in a manner worthy of him the Maker of all things.
For he ought not to have adulterated or polluted this worship with what we call “idolatry,” but what the many would describe by the term “superstition.” Now, according to a Hebrew figure of speech, it is said of God in the eighteenth Psalm, that “He made darkness His secret place,” to signify that those notions which should be worthily entertained of God are invisible and unknowable, because God conceals Himself in darkness, as it were, from those who cannot endure the splendours of His knowledge, or are incapable of looking at them, partly owing to the pollution of their understanding, which is clothed with the body of mortal lowliness, and partly owing to its feebler power of comprehending God.
And in order that it may appear that the knowledge of God has rarely been vouchsafed to men, and has been found in very few individuals, Moses is related to have entered into the darkness where God was. And again, with regard to Moses it is said: “Moses alone shall come near the Lord, but the rest shall not come near.” And again, that the prophet may show the depth of the doctrines which relate to God, and which is unattainable by those who do not possess the “Spirit which searches all things, even the deep things of God,” he added: “The abyss like a garment is His covering.” Nay, our Lord and Saviour, the Logos of God, manifesting that the greatness of the knowledge of the Father is appropriately comprehended and known pre-eminently by Him alone, and in the second place by those whose minds are enlightened by the Logos Himself and God, declares: “No man knows the Son, but the Father; neither knows any man the Father but the Son, and he to whomsoever the Son will reveal Him.” For no one can worthily know the “uncreated” and first-born of all created nature like the Father who begot Him, nor any one the Father like the living Logos, and His Wisdom and Truth. By sharing in Him who takes away from the Father what is called “darkness,” which He “made His secret place,” and “the abyss,” which is called His “covering,” and in this way unveiling the Father, every one knows the Father who is capable of knowing Him.
Source: Against Celsus (New Advent)