Some Truths Held Even by the Heathen. They Were, However, More Often Wrong Both in Religious Opinions and in Moral Practice. The Heathen Not to Be Followed in Their Ignorance of the Christian Mystery. The Heretics Perversely Prone to Follow Them
One may no doubt be wise in the things of God, even from one's natural powers, but only in witness to the truth, not in maintenance of error; (only) when one acts in accordance with, not in opposition to, the divine dispensation. For some things are known even by nature: the immortality of the soul, for instance, is held by many; the knowledge of our God is possessed by all. I may use, therefore, the opinion of a Plato, when he declares, “Every soul is immortal.” I may use also the conscience of a nation, when it attests the God of gods.
I may, in like manner, use all the other intelligences of our common nature, when they pronounce God to be a judge. “God sees,” (say they); and, “I commend you to God.” But when they say, “What has undergone death is dead,” and, “Enjoy life while you live,” and, “After death all things come to an end, even death itself;” then I must remember both that “the heart of man is ashes,” according to the estimate of God, and that the very “Wisdom of the world is foolishness,” (as the inspired word) pronounces it to be. Then, if even the heretic seek refuge in the depraved thoughts of the vulgar, or the imaginations of the world, I must say to him: Part company with the heathen, O heretic!
For although you are all agreed in imagining a God, yet while you do so in the name of Christ, so long as you deem yourself a Christian, you are a different man from a heathen: give him back his own views of things, since he does not himself learn from yours. Why lean upon a blind guide, if you have eyes of your own? Why be clothed by one who is naked, if you have put on Christ? Why use the shield of another, when the apostle gives you armour of your own? It would be better for him to learn from you to acknowledge the resurrection of the flesh, than for you from him to deny it; because if Christians must needs deny it, it would be sufficient if they did so from their own knowledge, without any instruction from the ignorant multitude.
He, therefore, will not be a Christian who shall deny this doctrine which is confessed by Christians; denying it, moreover, on grounds which are adopted by a man who is not a Christian. Take away, indeed, from the heretics the wisdom which they share with the heathen, and let them support their inquiries from the Scriptures alone: they will then be unable to keep their ground. For that which commends men's common sense is its very simplicity, and its participation in the same feelings, and its community of opinions; and it is deemed to be all the more trustworthy, inasmuch as its definitive statements are naked and open, and known to all. Divine reason, on the contrary, lies in the very pith and marrow of things, not on the surface, and very often is at variance with appearances.
Source: On the Resurrection of the Flesh (New Advent)