Against Heresies: Book V
Chapter 7: Given that Christ rose in our physical form, it implies that we too will be resurrected in the same way; because the promised resurrection applies not to naturally immortal spirits, but to naturally mortal bodies
In the same way that Christ rose in the substance of flesh and showed His disciples the marks of the nails and the wound in His side (which are the signs of the flesh that rose from the dead), it is said, "He will also raise us up by His own power." To the Romans, he says, "But if the Spirit of Him who raised Jesus from the dead lives in you, He who raised Christ from the dead will also make your mortal bodies alive." What, then, are mortal bodies? Can they be souls? No, because souls are incorporeal when compared to mortal bodies; for God "breathed into man's face the breath of life, and man became a living soul." The breath of life is an incorporeal thing.
Certainly, they cannot claim that the breath of life is mortal.
Therefore, David says, "My soul also shall live to Him," as if its essence were immortal. Nor can they say that the spirit is the mortal body. What then is there to which we can apply the term "mortal body," if not the thing that was formed, that is, the flesh, of which it is also said that God will make it alive? For it is the flesh that dies and decomposes, not the soul or the spirit.
To die means to lose vital power, to become breathless, lifeless, devoid of motion, and to decompose into the components from which it first acquired its substance.
But this does not happen to the soul, for it is the breath of life; nor to the spirit, for the spirit is simple and not composite, so it cannot decompose and is itself the life of those who receive it. We must conclude that death refers to the flesh, which, after the soul departs, becomes lifeless and breathless, decomposing gradually into the earth from which it was taken.
This, then, is what is mortal. And it is this of which he also says, "He shall also quicken your mortal bodies." Therefore, in relation to this, he says in the first Epistle to the Corinthians: "So too is the resurrection of the dead: it is sown in corruption, it rises in incorruption." He declares, "That which you sow cannot be quickened unless it first dies."
But what is it that, like a grain of wheat, is planted in the ground and decays, if not the bodies that are buried, which are also like seeds planted? For this reason, it is said, "It is sown in dishonor, it rises in glory." For what is more unworthy than dead flesh? Or, on the other hand, what is more glorious than that same flesh when it rises and partakes of incorruption? "It is sown in weakness, it is raised in power," signifying its own weakness, as it returns to the earth; but it is revived by the power of God, who raises it from the dead. "It is sown a natural body, it rises a spiritual body." He clearly teaches that this language refers not to the soul or spirit but to bodies that have turned into corpses. These are natural bodies, which partake of life but succumb to death when they lose it; then, rising through the Spirit’s power, they become spiritual bodies, possessing eternal life through the Spirit. "For now," he says, "we know in part, and we prophesy in part, but then face to face." This is also what Peter has said: "Whom not having seen, you love; though now you do not see him, yet believing, you rejoice with joy unspeakable." For our face shall see the face of the Lord and shall rejoice with indescribable joy—when it beholds its own Delight.