Let the ancient sages, then, make known their sayings to those who are capable of understanding them. Suppose that Plato, for example, the son of Ariston, in one of his Epistles, is discoursing about the “chief good,” and that he says, “The chief good can by no means be described in words, but is produced by long habit, and bursts forth suddenly as a light in the soul, as from a fire which had leapt forth.” We, then, on hearing these words, admit that they are well said, for it is God who revealed to men these as well as all other noble expressions.
And for this reason it is that we maintain that those who have entertained correct ideas regarding God, but who have not offered to Him a worship in harmony with the truth, are liable to the punishments which fall on sinners. For respecting such Paul says in express words: “The wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness; because that which may be known of God is manifest in them; for God has showed it unto them.
For the invisible things of Him from the creation of the world are clearly seen, being understood by the things that are made, even His eternal power and Godhead; so that they are without excuse: because that, when they knew God, they glorified Him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened. Professing themselves to be wise, they became fools, and changed the glory of the incorruptible God into an image made like to corruptible man, and to birds, and four-footed beasts, and creeping things.” The truth, then, is verily held (in unrighteousness), as our Scriptures testify, by those who are of opinion that “the chief good cannot be described in words,” but who assert that, “after long custom and familiar usage, a light becomes suddenly kindled in the soul, as if by a fire springing forth, and that it now supports itself alone.”
Source: Against Celsus (New Advent)