Catechetical instruction is necessary for those who preside over the mystery of godliness, so that the Church may increase through the addition of those who are being saved, as the faithful word of the teaching is brought to the hearing of unbelievers. Yet the same manner of instruction will not suit everyone who approaches the word. The catechesis itself must be adapted according to the differences among forms of religious belief: we keep our eyes on the same goal of the discourse, but do not use the same arguments in every case.
For the one who Judaizes has been preoccupied with one set of conceptions, and the one who lives according to Hellenism with another. The Anomoean, the Manichaean, the followers of Marcion, Valentinus, and Basilides, and the rest of the catalogue of those who have gone astray in the heresies are each preoccupied with their own conceptions; this makes it necessary to contend with their respective suppositions. For the manner of treatment must be adapted to the form of the disease.
You will not treat the Hellenist's polytheism and the Jew's unbelief concerning the Only-begotten God by the same means, nor will you overturn by the same arguments the deceptive doctrinal fictions of those who have gone astray in the heresies. The means by which one might correct Sabellius will not also benefit the Anomoean, nor will the argument against the Manichaean help the Jew. Rather, as has been said, one must attend to people's prior conceptions and frame the argument according to the error present in each person, setting out in each discussion certain principles and reasonable propositions so that, through what both sides acknowledge, the truth may be uncovered in due sequence.
Therefore, when the discussion is with someone who follows Hellenistic thought, it would be well to begin the argument in this way: does he believe that the divine exists, or does he agree with the teaching of the atheists? If he says that it does not exist, he may be led from the things ordered skillfully and wisely throughout the world to acknowledge that through them a certain power is manifested which transcends the whole. But if he does not doubt that the divine exists and yet in his thinking is carried toward a plurality of gods, let us use the following line of reasoning with him.
Does he consider the divine perfect or deficient? If, as is reasonable, he also testifies that perfection belongs to the divine nature, let us require him to acknowledge that it is perfect in every respect contemplated in the deity, so that the divine may not be regarded as a mixture of opposites, of deficiency and perfection.
Whether with respect to power, the conception of the good, wisdom, incorruptibility, eternity, or any other thought fitting to God that may belong to the contemplation, he will reasonably agree, by the logic of this argument, that perfection is contemplated in every respect in the divine nature. Once this is granted, it will no longer be difficult to turn a mind scattered among a plurality of gods toward the confession of one deity.
For if he grants that perfection in every respect is to be confessed concerning the subject under consideration, but says that there are many perfect beings characterized by the same things, it is altogether necessary, in the case of things distinguished by no variation but contemplated in the same characteristics, either to demonstrate what is particular to each or, if the mind apprehends nothing distinctive where there is no differentiating feature, not to suppose a distinction.
For if he can find no difference in terms of more and less—because the account of perfection does not admit diminution—nor in terms of worse and better, since one could no longer retain a conception of deity where the designation of the worse is not excluded; nor in terms of ancient and recent, since what does not always exist lies outside the conception of the divine; but the account of deity is one and the same, with no distinctive property reasonably found in any case, then the mistaken imagination of a plurality of gods must necessarily be pressed toward the confession of one deity.
For if goodness and justice, wisdom and power, are predicated in the same way, and incorruptibility, eternity, and every reverent conception are confessed in the same manner, then, as every difference in every respect is removed, the plurality of gods is necessarily removed from the doctrine along with it, since complete identity in all these respects turns faith toward the One.