Not to participation in mysteries, then, and to fellowship in the wisdom hidden in a mystery, which God ordained before the world to the glory of His saints, do we invite the wicked man, and the thief, and the housebreaker, and the poisoner, and the committer of sacrilege, and the plunderer of the dead, and all those others whom Celsus may enumerate in his exaggerating style, but such as these we invite to be healed.
For there are in the divinity of the word some helps towards the cure of those who are sick, respecting which the word says, “They that be whole need not a physician, but they that are sick;” others, again, which to the pure in soul and body exhibit “the revelation of the mystery, which was kept secret since the world began, but now is made manifest by the Scriptures of the prophets,” and “by the appearing of our Lord Jesus Christ,” which “appearing” is manifested to each one of those who are perfect, and which enlightens the reason in the true knowledge of things.
But as he exaggerates the charges against us, adding, after his list of those vile individuals whom he has mentioned, this remark, “What other persons would a robber summon to himself by proclamation?” we answer such a question by saying that a robber summons around him individuals of such a character, in order to make use of their villainy against the men whom they desire to slay and plunder. A Christian, on the other hand, even though he invite those whom the robber invites, invites them to a very different vocation, viz., to bind up these wounds by His word, and to apply to the soul, festering amid evils, the drugs obtained from the word, and which are analogous to the wine and oil, and plasters, and other healing appliances which belong to the art of medicine.
Source: Against Celsus (New Advent)