What We are to Understand by the Animal and Spiritual Body; Or of Those Who Die in Adam, And of Those Who are Made Alive in Christ
For as those bodies of ours, that have a living soul, though not as yet a quickening spirit, are called soul-informed bodies, and yet are not souls but bodies, so also those bodies are called spiritual,— yet God forbid we should therefore suppose them to be spirits and not bodies—which, being quickened by the Spirit, have the substance, but not the unwieldiness and corruption of flesh. Man will then be not earthly but heavenly,— not because the body will not be that very body which was made of earth, but because by its heavenly endowment it will be a fit inhabitant of heaven, and this not by losing its nature, but by changing its quality. The first man, of the earth earthy, was made a living soul, not a quickening spirit,— which rank was reserved for him as the reward of obedience. And therefore his body, which required meat and drink to satisfy hunger and thirst, and which had no absolute and indestructible immortality, but by means of the tree of life warded off the necessity of dying, and was thus maintained in the flower of youth—this body, I say, was doubtless not spiritual, but animal; and yet it would not have died but that it provoked God's threatened vengeance by offending. And though sustenance was not denied him even outside Paradise, yet, being forbidden the tree of life, he was delivered over to the wasting of time, at least in respect of that life which, had he not sinned, he might have retained perpetually in Paradise, though only in an animal body, till such time as it became spiritual in acknowledgment of his obedience.
Wherefore, although we understand that this manifest death, which consists in the separation of soul and body, was also signified by God when He said, “In the day you eat thereof you shall surely die,” it ought not on that account to seem absurd that they were not dismissed from the body on that very day on which they took the forbidden and death-bringing fruit. For certainly on that very day their nature was altered for the worse and vitiated, and by their most just banishment from the tree of life they were involved in the necessity even of bodily death, in which necessity we are born. And therefore the apostle does not say, “The body indeed is doomed to die on account of sin,” but he says, “The body indeed is dead because of sin.” Then he adds, “But if the Spirit of Him that raised up Jesus from the dead dwell in you, He that raised up Christ from the dead shall also quicken your mortal bodies by His Spirit that dwells in you.” Then accordingly shall the body become a quickening spirit which is now a living soul; and yet the apostle calls it “dead,” because already it lies under the necessity of dying. But in Paradise it was so made a living soul, though not a quickening spirit, that it could not properly be called dead, for, save through the commission of sin, it could not come under the power of death. Now, since God by the words, “Adam, where are you?” pointed to the death of the soul, which results when He abandons it, and since in the words, “Earth you are, and unto earth shall you return,” He signified the death of the body, which results when the soul departs from it, we are led, therefore, to believe that He said nothing of the second death, wishing it to be kept hidden, and reserving it for the New Testament dispensation, in which it is most plainly revealed. And this He did in order that, first of all, it might be evident that this first death, which is common to all, was the result of that sin which in one man became common to all. But the second death is not common to all, those being excepted who were “called according to His purpose. For whom He did foreknow, He also did pre destinate to be conformed to the image of His Son, that He might be the first-born among many brethren.” Those the grace of God has, by a Mediator, delivered from the second death.
Thus the apostle states that the first man was made in an animal body. For, wishing to distinguish the animal body which now is from the spiritual, which is to be in the resurrection, he says, “It is sown in corruption, it is raised in incorruption: it is sown in dishonor, it is raised in glory: it is sown in weakness, it is raised in power: it is sown a natural body, it is raised a spiritual body.” Then, to prove this, he goes on, “There is a natural body, and there is a spiritual body.” And to show what the animated body is, he says, “Thus it was written, The first man Adam was made a living soul, the last Adam was made a quickening spirit.” He wished thus to show what the animated body is, though Scripture did not say of the first man Adam, when his soul was created by the breath of God, “Man was made in an animated body,” but “Man was made a living soul.” By these words, therefore, “The first man was made a living soul,” the apostle wishes man's animated body to be understood. But how he wishes the spiritual body to be understood he shows when he adds, “But the last Adam was made a quickening spirit,” plainly referring to Christ, who has so risen from the dead that He cannot die any more. He then goes on to say, “But that was not first which is spiritual, but that which is natural; and afterward that which is spiritual.” And here he much more clearly asserts that he referred to the animal body when he said that the first man was made a living soul, and to the spiritual when he said that the last man was made a quickening spirit. The animal body is the first, being such as the first Adam had, and which would not have died had he not sinned, being such also as we now have, its nature being changed and vitiated by sin to the extent of bringing us under the necessity of death, and being such as even Christ condescended first of all to assume, not indeed of necessity, but of choice; but afterwards comes the spiritual body, which already is worn by anticipation by Christ as our head, and will be worn by His members in the resurrection of the dead.
Source: City of God (New Advent)