Nicene and Post-Nicene Fathers, Vol. II:
City of God: Chapter 24

Chapter 24.—Of the One Only True Principle Which Alone Purifies and Renews Human Nature.

Accordingly, when we speak of God, we do not affirm two or three principles, no more than we are at liberty to affirm two or three p. 195 gods; although, speaking of each, of the Father, or of the Son, or of the Holy Ghost, we confess that each is God:  and yet we do not say, as the Sabellian heretics say, that the Father is the same as the Son, and the Holy Spirit the same as the Father and the Son; but we say that the Father is the Father of the Son, and the Son the Son of the Father, and that the Holy Spirit of the Father and the Son is neither the Father nor the Son.  It was therefore truly said that man is cleansed only by a Principle, although the Platonists erred in speaking in the plural of principles.  But Porphyry, being under the dominion of these envious powers, whose influence he was at once ashamed of and afraid to throw off, refused to recognize that Christ is the Principle by whose incarnation we are purified.  Indeed he despised Him, because of the flesh itself which He assumed, that He might offer a sacrifice for our purification,—a great mystery, unintelligible to Porphyry’s pride, which that true and benignant Redeemer brought low by His humility, manifesting Himself to mortals by the mortality which He assumed, and which the malignant and deceitful mediators are proud of wanting, promising, as the boon of immortals, a deceptive assistance to wretched men.  Thus the good and true Mediator showed that it is sin which is evil, and not the substance or nature of flesh; for this, together with the human soul, could without sin be both assumed and retained, and laid down in death, and changed to something better by resurrection.  He showed also that death itself, although the punishment of sin, was submitted to by Him for our sakes without sin, and must not be evaded by sin on our part, but rather, if opportunity serves, be borne for righteousness’ sake.  For he was able to expiate sins by dying, because He both died, and not for sin of His own.  But He has not been recognized by Porphyry as the Principle, otherwise he would have recognized Him as the Purifier.  The Principle is neither the flesh nor the human soul in Christ but the Word by which all things were made.  The flesh, therefore, does not by its own virtue purify, but by virtue of the Word by which it was assumed, when “the Word became flesh and dwelt among us.” 420   For speaking mystically of eating His flesh, when those who did not understand Him were offended and went away, saying, “This is an hard saying, who can hear it?” He answered to the rest who remained, “It is the Spirit that quickeneth; the flesh profiteth nothing.” 421   The Principle, therefore, having assumed a human soul and flesh, cleanses the soul and flesh of believers.  Therefore, when the Jews asked Him who He was, He answered that He was the Principle. 422   And this we carnal and feeble men, liable to sin, and involved in the darkness of ignorance, could not possibly understand, unless we were cleansed and healed by Him, both by means of what we were, and of what we were not.  For we were men, but we were not righteous; whereas in His incarnation there was a human nature, but it was righteous, and not sinful.  This is the mediation whereby a hand is stretched to the lapsed and fallen; this is the seed “ordained by angels,” by whose ministry the law also was given enjoining the worship of one God, and promising that this Mediator should come.

Footnotes

John 1.14.

John 6.60-64.

John 8.25; or “the beginning,” following a different reading from ours.