We are careful not to oppose fair arguments even if they proceed from those who are not of our faith; we strive not to be captious, or to seek to overthrow any sound reasonings. But here we have to reply to those who slander the character of persons wishing to do their best in the service of God, who accepts the faith which the meanest place in Him, as well as the more refined and intelligent piety of the learned; seeing that both alike address to the Creator of the world their prayers and thanksgivings through the High Priest who has set before men the nature of pure religion.
We say, then, that those who are stigmatized as “lamed and mutilated in spirit,” as “living only for the sake of the body which is dead,” are persons whose endeavour it is to say with sincerity: “For though we live in the flesh, we do not war according to the flesh; for the weapons of our warfare are not fleshly, but mighty through God.” It is for those who throw out such vile accusations against men who desire to be God's servants, to beware lest, by the calumnies which they cast upon others who strive to live well, they “lame” their own souls, and “mutilate” the inner man, by severing from it that justice and moderation of mind which the Creator has planted in the nature of all His rational creatures.
As for those, however, who, along with other lessons given by the Divine Word, have learned and practised this, “when reviled to bless, when persecuted to endure, when defamed to entreat,” they may be said to be walking in spirit in the ways of uprightness, to be purifying and setting in order the whole soul. They distinguish— and to them the distinction is not one of words merely— between “substance,” or that which is, and that which is “becoming;” between things apprehended by reason, and things apprehended by sense; and they connect truth with the one, and avoid the errors arising out of the other; looking, as they have been taught, not at the things “becoming” or phenomenal, which are seen, and therefore temporary, but at better things than these, whether we call them “substance,” or “spiritual” things, as being apprehended by reason, or “invisible,” because they lie out of the reach of the senses.
The disciples of Jesus regard these phenomenal things only that they may use them as steps to ascend to the knowledge of the things of reason. For “the invisible things of God,” that is, the objects of the reason, “from the creation of the world are clearly seen” by the reason, “being understood by the things that are made.” And when they have risen from the created things of this world to the invisible things of God, they do not stay there; but after they have sufficiently exercised their minds upon these, and have understood their nature, they ascend to “the eternal power of God,” in a word, to His divinity.
For they know that God, in His love to men, has “manifested” His truth, and “that which is known of Him,” not only to those who devote themselves to His service, but also to some who are far removed from the purity of worship and service which He requires; and that some of those who by the providence of God had attained a knowledge of these truths, were yet doing things unworthy of that knowledge, and “holding the truth in unrighteousness,” and who are unable to find any excuse before God after the knowledge of such great truths which He has given them.
Source: Against Celsus (New Advent)