Even to this objection we are not at a loss for an answer consistent with our idea of God. You ask the reason why God was born among men. If you take away from life the benefits that come to us from God, you would not be able to tell me what means you have of arriving at any knowledge of Deity. In the kindly treatment of us we recognize the benefactor; that is, from observation of that which happens to us, we conjecture the disposition of the person who operates it. If, then, love of man be a special characteristic of the Divine nature, here is the reason for which you are in search, here is the cause of the presence of God among men.
Our diseased nature needed a healer. Man in his fall needed one to set him upright. He who had lost the gift of life stood in need of a life-giver, and he who had dropped away from his fellowship with good wanted one who would lead him back to good. He who was shut up in darkness longed for the presence of the light. The captive sought for a ransomer, the fettered prisoner for some one to take his part, and for a deliverer he who was held in the bondage of slavery. Were these, then, trifling or unworthy wants to importune the Deity to come down and take a survey of the nature of man, when mankind was so miserably and pitiably conditioned?
“But,” it is replied, “man might have been benefited, and yet God might have continued in a passionless state. Was it not possible for Him Who in His wisdom framed the universe, and by the simple impulse of His will brought into subsistence that which was not, had it so pleased Him, by means of some direct Divine command to withdraw man from the reach of the opposing power, and bring him back to his primal state? Whereas He waits for long periods of time to come round, He submits Himself to the condition of a human body, He enters upon the stage of life by being born, and after passing through each age of life in succession, and then tasting death, at last, only by the rising again of His own body, accomplishes His object—as if it was not optional to Him to fulfil His purpose without leaving the height of His Divine glory, and to save man by a single command, letting those long periods of time alone.”
Needful, therefore, is it that in answer to objections such as these we should draw out the counter-statement of the truth, in order that no obstacle may be offered to the faith of those persons who will minutely examine the reasonableness of the gospel revelation. In the first place, then, as has been partially discussed before, let us consider what is that which, by the rule of contraries, is opposed to virtue. As darkness is the opposite of light, and death of life, so vice, and nothing else besides, is plainly the opposite of virtue.
For as in the many objects in creation there is nothing which is distinguished by its opposition to light or life, but only the peculiar ideas which are their exact opposites, as darkness and death— not stone, or wood, or water, or man, or anything else in the world—so, in the instance of virtue, it cannot be said that any created thing can be conceived of as contrary to it, but only the idea of vice. If, then, our Faith preached that the Deity had been begotten under vicious circumstances, an opportunity would have been afforded the objector of running down our belief, as that of persons who propounded incongruous and absurd opinions with regard to the Divine nature.
For, indeed, it were blasphemous to assert that the Deity, Which is very wisdom, goodness, incorruptibility, and every other exalted thing in thought or word, had undergone change to the contrary. If, then, God is real and essential virtue, and no mere existence of any kind is logically opposed to virtue, but only vice is so; and if the Divine birth was not into vice, but into human existence; and if only vicious weakness is unseemly and shameful— and with such weakness neither was God born, nor had it in His nature to be born—why are they scandalized at the confession that God came into touch with human nature, when in relation to virtue no contrariety whatever is observable in the organization of man?
For neither Reason, nor Understanding, nor Receptivity for science, nor any other like quality proper to the essence of man, is opposed to the principle of virtue.
Source: The Great Catechism (New Advent)