Against Praxeas by Tertullian
Chapter XXV.--The Paraclete, or Holy Ghost He is Distinct from the Father and the Son as to Their Personal Existence. One and Inseparable from Them as to Their Divine Nature. Other Quotations Out of St. John's Gospel.
What follows Philip's question, and the Lord's whole treatment of it, to the end of John's Gospel, continues to furnish us with statements of the same kind, distinguishing the Father and the Son, with the properties of each. Then there is the Paraclete or Comforter, also, which He promises to pray for to the Father, and to send from heaven after He had ascended to the Father. He is called |another Comforter,| indeed; but in what way He is another we have already shown, |He shall receive of mine,| says Christ, just as Christ Himself received of the Father's. Thus the connection of the Father in the Son, and of the Son in the Paraclete, produces three coherent Persons, who are yet distinct One from Another. These Three are one essence, not one Person, as it is said, |I and my Father are One,| in respect of unity of substance not singularity of number. Run through the whole Gospel, and you will find that He whom you believe to be the Father (described as acting for the Father, although you, for your part, forsooth, suppose that |the Father, being the husbandman,| must surely have been on earth) is once more recognised by the Son as in heaven, when, |lifting up His eyes thereto,| He commended His disciples to the safe-keeping of the Father. We have, moreover, in that other Gospel a clear revelation, i.e. of the Son's distinction from the Father, |My God, why hast Thou forsaken me?| and again, (in the third Gospel,) |Father, into Thy hands I commend my spirit.| But even if (we had not these passages, we meet with satisfactory evidence) after His resurrection and glorious victory over death. Now that all the restraint of His humiliation is taken away, He might, if possible, have shown Himself as the Father to so faithful a woman (as Mary Magdalene) when she approached to touch Him, out of love, not from curiosity, nor with Thomas' incredulity. But not so; Jesus saith unto her, |Touch me not, for I am not yet ascended to my Father; but go to my brethren| (and even in this He proves Himself to be the Son; for if He had been the Father, He would have called them His children, (instead of His brethren), |and say unto them, I ascend unto my Father and your Father, and to my God and your God.| Now, does this mean, I ascend as the Father to the Father, and as God to God? Or as the Son to the Father, and as the Word to God? Wherefore also does this Gospel, at its very termination, intimate that these things were ever written, if it be not, to use its own words, |that ye might believe that Jesus Christ is the Son of God?| Whenever, therefore, you take any of the statements of this Gospel, and apply them to demonstrate the identity of the Father and the Son, supposing that they serve your views therein, you are contending against the definite purpose of the Gospel. For these things certainly are not written that you may believe that Jesus Christ is the Father, but the Son.