For Scripture testifies, in regard to those who have a knowledge of those things of which Celsus speaks, and who profess a philosophy founded on these principles, that they, “when they knew God, glorified Him not as God, neither were thankful, but became vain in their imaginations;” and notwithstanding the bright light of knowledge with which God had enlightened them, “their foolish heart” was carried away, and became “darkened.” Thus we may see how those who accounted themselves wise gave proofs of great folly, when, after such grand arguments delivered in the schools on God and on things apprehended by the reason, they “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.” As, then, they lived in a way unworthy of the knowledge which they had received from God, His providence leaving them to themselves, they were given “up to uncleanness, through the lusts of their own hearts to dishonour their own bodies,” in shamelessness and licentiousness, because they “changed the truth of God into a lie, and worshipped and served the creature more than the Creator.”
Source: Against Celsus (New Advent)