John 15:26,27

Ver 26. But when the Comforter is come, whom I will send to you from the Father, even the Spirit of truth, which proceeds from the Father, he shall testify of me. 27. And you also shall bear witness, because you have been with me from the beginning.

CHRYS. The disciples might say, If they have heard words from Thee, such as none other has spoken, if they have seen works of Him, such as none other has done, and yet have not been convinced, but have hated your Father, and you with Him, why do you send us to preach? How shall we be believed? Such thoughts as these He now answers: But when the Comforter is come, Whom I will send to you from the Father, even the Spirit of Truth which proceeds from the Father, he shall testify of Me.

AUG. As if He said, Seeing Me, they hated and killed Me; but the Comforter shall give such testimony concerning Me as shall make them believe, though they see Me not. And because He shall testify, you shall testify also:

And you also shall bear witness; He will inspire your hearts, and you shall proclaim with your voices. And you will preach what you know, Because you have been with Me from the beginning; which now you do not do, because you have not yet the fullness of the Spirit. But the love of God shall then be shed abroad in your hearts by the Spirit which shall be given you, and shall make you confident witnesses to Me. The Holy Spirit by His testimony made others testify, taking away fear from the friends of Christ's, and converting the hatred of His enemies into love.

DIDYMUS. The Holy Spirit He calls the Comforter, a name taken from His office, which is not only to relieve the sorrows of the faithful, but to fill them with unspeakable joy. Everlasting gladness is in those hearts, in which the Spirit dwells. The Spirit, the Comforter, is sent by the Son, not as Angels, or Prophets, or Apostles, are sent, but as the Spirit must be sent which is of one nature with the Divine wisdom and power that sends Him. The Son when sent by the Father, is not separated from Him, but abides in the Father, and the Father in Him. In the same way the Holy Spirit is not sent by the Son, and proceeds from the Father, in the sense of change of place. For as the Father's nature, being incorporeal, is not local, so neither has the Spirit of truth, Who is incorporeal also, and superior to all created things, a local nature.

CHRYS. He calls Him not the Holy Spirit, but the Spirit of truth, to show the perfect faith that was due to Him. He knew that He proceeds from the Father, for He knew all things; He knew where He Himself came from, as He says of Himself above, I know whence I came, and whither l go (John 8:14).

DIDYMUS. He does not say, from God, or, from the Almighty, but, from the Father, because though the Father and God Almighty are the same, yet the Spirit of truth properly proceeds from God, as the Father, the Begetter. The Father and the Son together send the Spirit of truth: He comes by the will both of the Father and the Son.

THEOPHYL. Elsewhere He says that the Father sends the Spirit; now He says He does: Whom I will send to you, thus declaring the equality of the Father and the Son. That He might not be thought however to be opposed to the Father, and to be another and rival source, as it were, of the Spirit, He adds, From the Father, i.e., the Father agreeing, and taking an equal part in sending Him. When it is said that He proceeds, do not understand His procession to be an external mission, such as is given to ministering spirits, but a certain peculiar, and distinct procession, such as is true of the Holy Spirit alone. To proceed is not the same as being sent, but is the essential nature of the Holy Ghost, as coming from the Father.

AUG. If it be asked here whether the Holy Ghost proceeds from the Son also, we may answer thus: The Son is the Son of the Father alone, and the Father is the Father of the Son only; but the Holy Spirit is not the Spirit of one, but of both; since Christ Himself said, The Spirit of your Father which speaks in you (Matthew 10:20). And the Apostle says, God has sent the Spirit of His Son into your hearts (Galatians 4:6). This indeed, I think, is the reason why He is called peculiarly the Spirit. For both of the Father and the Son separately we may pronounce, that each is a Spirit. But what each is separately in a general sense, He who is not either one separately, but the union of both, is spiritually. But if the Holy Spirit is the Spirit of the Son, why should we not believe that He proceeds from the Son? Indeed if He did not proceed from the Son, Christ would not after the resurrection have breathed on His disciples, and said, Receive you the Holy Ghost. This too is what is meant by the virtue which went out of Him, and healed all. If the Holy Ghost then proceeds both from the Father and the Son, why does Christ say, Who proceeds from the Father? He says it in accordance with His general way of referring all that He has to Him from whom He is; as where He says, My doctrine is not Mine, but His that sent Me. If the doctrine was His, which He says was not His own, but the Father's, much more does the Holy Spirit proceed from Him, consistently with His proceeding from the Father. From whom the Son has His Godhead, from Him He has it that the Holy Ghost proceeds from Him. And this explains why the Holy Ghost is not said to be born, but to proceed. For if He were born, He would be the Son of both Father and Son, an absurd supposition; for if two together have a Son, those two must be father and mother. But to imagine any such relation as this between God the Father, and God the Son, is monstrous. Even the human offspring does not proceed from father or mother at the same time; when it proceeds from the father, it does not proceed from the mother. Whereas the Holy Spirit does not proceed from the Father into the Son, and from the Son into the creature to be sanctified; but proceeds from Father and Son at once. And if the Father is life, and the Son is life, so the Holy Ghost is life also. Just then as the Father when He had life in Himself, gave also to the Son to have life in Himself; so He gave to the Son also that life should proceed from Him, even as it proceeded from Himself.