Irenaeus

If, however, any one say, "What then? Could not God have exhibited man as perfect from beginning?" let him know that, inasmuch as God is indeed always the same and unbegotten as respects Himself, all things are possible to Him. But created things must be inferior to Him who created them, from the very fact of their later origin; for it was not possible for things recently created to have been uncreated. But inasmuch as they are not uncreated, for this very reason do they come short of the perfect. Because, as these things are of later date, so are they infantile; so are they unaccustomed to, and unexercised in, perfect discipline. For as it certainly is in the power of a mother to give strong food to her infant, [but she does not do so], as the child is not yet able to receive more substantial nourishment; so also it was possible for God Himself to have made man perfect from the first, but man could not receive this [perfection], being as yet an infant. And for this cause our Lord in these last times, when He had summed up all things into Himself, came to us, not as He might have come, but as we were capable of beholding Him. He might easily have come to us in His immortal glory, but in that case we could never have endured the greatness of the glory; and therefore it was that He, who was the perfect bread of the Father, offered Himself to us as milk, [because we were] as infants. He did this when He appeared as a man, that we, being nourished, as it were, from the breast of His flesh, and having, by such a course of milk nourishment, become accustomed to eat and drink the Word of God, may be able also to contain in ourselves the Bread of immortality, which is the Spirit of the Father.

And on this account does Paul declare to the Corinthians, "I have fed you with milk, not with meat, for hitherto ye were not able to bear it." That is, ye have indeed learned the advent of our Lord as a man; nevertheless, because of your infirmity, the Spirit of the Father has not as yet rested upon you. "For when envying and strife," he says, "and dissensions are among you, are ye not carnal, and walk as men?" That is, that the Spirit of the Father was not yet with them, on account of their imperfection and shortcomings of their walk in life. As, therefore, the apostle had the power to give them strong meat-for those upon whom the apostles laid hands received the Holy Spirit, who is the food of life [eternal]-but they were not capable of receiving it, because they had the sentient faculties of the soul still feeble and undisciplined in the practice of things pertaining to God; so, in like manner, God had power at the beginning to grant perfection to man; but as the latter was only recently created, he could not possibly have received it, or even if he had received it, could he have contained it, or containing it, could he have retained it. It was for this reason that the Son of God, although He was perfect, passed through the state of infancy in common with the rest of mankind, partaking of it thus not for His own benefit, but for that of the infantile stage of man's existence, in order that man might be able to receive Him. There was nothing, therefore, impossible to and deficient in God, [implied in the fact] that man was not an uncreated being; but this merely applied to him who was lately created, [namely] man.