Still, in his examination of the amount of justice and wisdom discoverable in this Dispensation a person is, perhaps, induced to entertain the thought that it was by means of a certain amount of deceit that God carried out this scheme on our behalf. For that not by pure Deity alone, but by Deity veiled in human nature, God, without the knowledge of His enemy, got within the lines of him who had man in his power, is in some measure a fraud and a surprise; seeing that it is the peculiar way with those who want to deceive to divert in another direction the expectations of their intended victims, and then to effect something quite different from what these latter expected.
But he who has regard for truth will agree that the essential qualities of justice and wisdom are before all things these; viz. of justice, to give to every one according to his due; of wisdom, not to pervert justice, and yet at the same time not to dissociate the benevolent aim of the love of mankind from the verdict of justice, but skilfully to combine both these requisites together, in regard to justice returning the due recompense, in regard to kindness not swerving from the aim of that love of man.
Let us see, then, whether these two qualities are not to be observed in that which took place. That repayment, adequate to the debt, by which the deceiver was in his turn deceived, exhibits the justice of the dealing, while the object aimed at is a testimony to the goodness of Him who effected it. It is, indeed, the property of justice to assign to every one those particular results of which he has sunk already the foundations and the causes, just as the earth returns its harvests according to the kinds of seeds thrown into it; while it is the property of wisdom, in its very manner of giving equivalent returns, not to depart from the kinder course.
Two persons may both mix poison with food, one with the design of taking life, the other with the design of saving that life; the one using it as a poison, the other only as an antidote to poison; and in no way does the manner of the cure adopted spoil the aim and purpose of the benefit intended; for although a mixture of poison with the food may be effected by both of these persons alike, yet looking at their intention we are indignant with the one and approve the other; so in this instance, by the reasonable rule of justice, he who practised deception receives in return that very treatment, the seeds of which he had himself sown of his own free will.
He who first deceived man by the bait of sensual pleasure is himself deceived by the presentment of the human form. But as regards the aim and purpose of what took place, a change in the direction of the nobler is involved; for whereas he, the enemy, effected his deception for the ruin of our nature, He Who is at once the just, and good, and wise one, used His device, in which there was deception, for the salvation of him who had perished, and thus not only conferred benefit on the lost one, but on him, too, who had wrought our ruin.
For from this approximation of death to life, of darkness to light, of corruption to incorruption, there is effected an obliteration of what is worse, and a passing away of it into nothing, while benefit is conferred on him who is freed from those evils. For it is as when some worthless material has been mixed with gold, and the gold-refiners burn up the foreign and refuse part in the consuming fire, and so restore the more precious substance to its natural lustre: (not that the separation is effected without difficulty, for it takes time for the fire by its melting force to cause the baser matter to disappear; but for all that, this melting away of the actual thing that was embedded in it to the injury of its beauty is a kind of healing of the gold.)
In the same way when death, and corruption, and darkness, and every other offshoot of evil had grown into the nature of the author of evil, the approach of the Divine power, acting like fire, and making that unnatural accretion to disappear, thus by purgation of the evil becomes a blessing to that nature, though the separation is agonizing. Therefore even the adversary himself will not be likely to dispute that what took place was both just and salutary, that is, if he shall have attained to a perception of the boon.
For it is now as with those who for their cure are subjected to the knife and the cautery; they are angry with the doctors, and wince with the pain of the incision; but if recovery of health be the result of this treatment, and the pain of the cautery passes away, they will feel grateful to those who have wrought this cure upon them. In like manner, when, after long periods of time, the evil of our nature, which now is mixed up with it and has grown with its growth, has been expelled, and when there has been a restoration of those who are now lying in Sin to their primal state, a harmony of thanksgiving will arise from all creation, as well from those who in the process of the purgation have suffered chastisement, as from those who needed not any purgation at all.
These and the like benefits the great mystery of the Divine incarnation bestows. For in those points in which He was mingled with humanity, passing as He did through all the accidents proper to human nature, such as birth, rearing, growing up, and advancing even to the taste of death, He accomplished all the results before mentioned, freeing both man from evil, and healing even the introducer of evil himself. For the chastisement, however painful, of moral disease is a healing of its weakness.
Source: The Great Catechism (New Advent)