15. Now how it is that we are in Him through the sacrament of the flesh and blood bestowed upon us, He Himself testifies, saying, And the world will no longer see Me, but ye shall see Me; because I live ye shall live also; because I am in My Father, and ye in Me, and I in you [905] . If He wished to indicate a mere unity of will, why did He set forth a kind of gradation and sequence in the completion of the unity, unless it were that, since He was in the Father through the nature of Deity, and we on the contrary in Him through His birth in the body, He would have us believe that He is in us through the mystery of the sacraments? and thus there might be taught a perfect unity through a Mediator, whilst, we abiding in Him, He abode in the Father, and as abiding in the Father abode also in us; and so we might arrive at unity with the Father, since in Him Who dwells naturally in the Father by birth, we also dwell naturally, while He Himself abides naturally in us also.
16. Again, how natural this unity is in us He has Himself testified on this wise,--He who eateth My flesh and drinketh My blood abideth in Me, and I in him [906] . For no man shall dwell in Him, save him in whom He dwells Himself, for the only flesh which He has taken to Himself is the flesh of those who have taken His. Now He had already taught before the sacrament of this perfect unity, saying, As the living Father sent Me, and I live through the Father, so he that eateth My flesh shall himself also live through Me [907] . So then He lives through the Father, and as He lives through the Father in like manner we live through His flesh. For all comparison is chosen to shape our understanding, so that we may grasp the subject of which we treat by help of the analogy set before us. This is the cause of our life that we have Christ dwelling within our carnal selves through the flesh, and we shall live through Him in the same manner as He lives through the Father. If, then, we live naturally through Him according to the flesh, that is, have partaken of the nature of His flesh, must He not naturally have the Father within Himself according to the Spirit since He Himself lives through the Father? And He lives through the Father because His birth has not implanted in Him an alien and different nature inasmuch as His very being is from Him yet is not divided from Him by any barrier of an unlikeness of nature, for within Himself He has the Father through the birth in the power of the nature.
17. I have dwelt upon these facts because the heretics falsely maintain that the union between Father and Son is one of will only, and make use of the example of our own union with God, as though we were united to the Son and through the Son to the Father by mere obedience and a devout will, and none of the natural verity of communion were vouchsafed us through the sacrament of the Body and Blood; although the glory of the Son bestowed upon us through the Son abiding in us after the flesh, while we are united in Him corporeally and inseparably, bids us preach the mystery of the true and natural unity.
18. So we have made our reply to the folly of our violent opponents, merely to prove the emptiness of their falsehoods and so prevent them from misleading the unwary by the error of their vain and foolish statements. But the faith of the Gospel did not of necessity require our answer. The Lord prayed on our behalf for our union with God, but God keeps His own unity and abides in it. It is not through any mysterious appointment of God that they are one, but through a birth of nature, for God loses nothing in begetting Him from Himself. They are one, for the things which are not plucked out of His hand are not plucked out of the hand of the Father [908] , for, when He is known, the Father is known, for, when He is seen, the Father is seen, for what He speaks the Father speaks as abiding in Him, for in His works the Father works, for He is in the Father and the Father in Him [909] . This proceeds from no creation but from birth; it is not brought about by will but by power; it is no agreement of mind that speaks, it is nature; because to be created and to be born are not one and the same, any more than to will and to be able; neither is it the same thing to agree and to abide.
19. Thus we do not deny a unanimity between the Father and the Son,--for heretics are accustomed to utter this falsehood, that since we do not accept concord by itself as the bond of unity we declare Them to be at variance. But let them listen how it is that we do not deny such a unanimity. The Father and the Son are one in nature, honour, power, and the same nature cannot will things that are contrary. Moreover, let them listen to the testimony of the Son as touching the unity of nature between Himself and the Father, for He says, When that advocate is come, Whom I shall send to you from the Father, the Spirit of truth Who proceedeth from the Father, He shall testify of Me [910] . The Advocate shall come and the Son shall send Him from the Father, and He is the Spirit of truth Who proceedeth from the Father. Let the whole following of heretics arouse the keenest powers of their wit; let them now seek for what lies they can tell to the unlearned, and declare what that is which the Son sends from the Father. He Who sends manifests His power in that which He sends. But as to that which He sends from the Father, how shall we regard it, as received or sent forth or begotten? For His words that He will send from the Father must imply one or other of these modes of sending. And He will send from the Father that Spirit of truth which proceedeth from the Father; He therefore cannot be the Recipient, since He is revealed as the Sender. It only remains to make sure of our conviction on the point, whether we are to believe an egress of a co-existent Being, or a procession of a Being begotten.
20. For the present I forbear to expose their licence of speculation, some of them holding that the Paraclete Spirit comes from the Father or from the Son. For our Lord has not left this in uncertainty, for after these same words He spoke thus,--I have yet many things to say unto you, but ye cannot bear them now. When He, the Spirit of truth, is come, He shall guide you into all truth: for He shall not speak from Himself: but what things soever He shall hear, these shall He speak; and He shall declare unto you the things that are to come. He shall glorify Me: for He shall receive of Mine and shall declare it unto you. All things whatsoever the Father hath are Mine: therefore said I, He shall receive of Mine and shall declare it unto you [911] . Accordingly He receives from the Son, Who is both sent by Him, and proceeds from the Father. Now I ask whether to receive from the Son is the same thing as to proceed from the Father. But if one believes that there is a difference between receiving from the Son and proceeding from the Father, surely to receive from the Son and to receive from the Father will be regarded as one and the same thing. For our Lord Himself says, Because He shall receive of Mine and shall declare it unto you. All things whatsoever the Father hath are Mine: therefore said I, He shall receive of Mine and shall declare it unto you. That which He will receive,--whether it will be power, or excellence, or teaching,--the Son has said must be received from Him, and again He indicates that this same thing must be received from the Father. For when He says that all things whatsoever the Father hath are His, and that for this cause He declared that it must be received from His own, He teaches also that what is received from the Father is yet received from Himself, because all things that the Father hath are His. Such a unity admits no difference, nor does it make any difference from whom that is received, which given by the Father is described as given by the Son. Is a mere unity of will brought forward here also? All things which the Father hath are the Son's, and all things which the Son hath are the Father's. For He Himself saith, And all Mine are Thine, and Thine are Mine [912] . It is not yet the place to shew why He spoke thus, For He shall receive of Mine: for this points to some subsequent time, when it is revealed that He shall receive. Now at any rate He says that He will receive of Himself, because all things that the Father had were His. Dissever if thou canst the unity of the nature, and introduce some necessary unlikeness through which the Son may not exist in unity of nature. For the Spirit of truth proceedeth from the Father and is sent from the Father by the Son. All things that the Father hath are the Son's; and for this cause whatever He Who is to be sent shall receive, He shall receive from the Son, because all things that the Father hath are the Son's. The nature in all respects maintains its law, and because Both are One that same Godhead is signified as existing in Both through generation and nativity; since the Son affirms that that which the Spirit of truth shall receive from the Father is to be given by Himself. So the frowardness of heretics must not be allowed an unchecked licence of impious beliefs, in refusing to acknowledge that this saying of the Lord,--that because all things which the Father hath are His, therefore the Spirit of truth shall receive of Him,--is to be referred to unity of nature.
21. Let us listen to that chosen vessel and teacher of the Gentiles, when he had already commended the faith of the people of Rome because of their understanding of the truth. For wishing to teach the unity of nature in the case of the Father and the Son, he speaks thus, But ye are not in the flesh but in the Spirit, if indeed the Spirit of God is in you. But if any have not the Spirit of Christ, he is none of His. But if Christ is in you, the body indeed is dead through sin, but the Spirit is life through righteousness. But if the Spirit of Him Who raised up Christ from the dead dwelleth in you; He Who raised up Christ from the dead shall also quicken your mortal bodies, because of His Spirit Who dwelleth in you [913] . We are all spiritual if the Spirit of God dwells in us. But this Spirit of God is also the Spirit of Christ, and though the Spirit of Christ is in us, yet His Spirit is also in us Who raised Christ from the dead, and He Who raised Christ from the dead shall quicken our mortal bodies also on account of His Spirit that dwelleth in us. We are quickened therefore on account of the Spirit of Christ that dwelleth in us, through Him Who raised Christ from the dead. And since the Spirit of Him Who raised Christ from the dead dwells in us, and yet the Spirit of Christ is in us, nevertheless the Spirit Which is in us cannot but be the Spirit of God. Separate, then, O heretic, the Spirit of Christ from the Spirit of God, and the Spirit of Christ raised from the dead from the Spirit of God Which raises Christ from the dead; when the Spirit of Christ that dwelleth in us is the Spirit of God, and when the Spirit of Christ Who was raised from the dead is yet the Spirit of God Who raises Christ from the dead.
22. And now I ask whether thou thinkest that in the Spirit of God is signified a nature or a property belonging to a nature. For a nature is not identical with a thing belonging to it, just as neither is a man identical with what belongs to a man, nor fire with what belongs to fire itself, and in like manner God is not the same as that which belongs to God.