18 Where, then, will you find the proof required to show that it is from the Paraclete that you have learned that the Gospels were not written by the apostles? On the other hand, we have proof that the Holy Spirit, the Paraclete, came immediately after the glorification of Jesus. For "He was not yet given, because that Jesus was not yet glorified." We have proof also that He leads into all truth, for the only way to truth is by love, and "the love of God," says the apostle, "is shed abroad in our hearts by the Holy Ghost who is given unto us." We show, too, that in the words, "when that which is perfect has come," Paul spoke of the perfection in the enjoyment of eternal life.
For in the same place he says: "Now we see through a glass darkly, but then face to face." You cannot reasonably maintain that we see God face to face here. Therefore that which is perfect has not come to you. It is thus clear what the apostle thought on this subject. This perfection will not come to the saints till the accomplishment of what John speaks of: "Now we are the sons of God, and it does not yet appear what we shall be; but we know that when it shall appear we shall be like Him, for we shall see Him as He is." Then we shall be led into all truth by the Holy Spirit, of which we have now received the pledge.
Again, the words, "The world cannot receive Him," plainly point to those who are usually called the world in Scripture— the lovers of the world, the wicked, or carnal; of whom the apostle says: "The natural man perceives not the things which are of the Spirit of God." Those are said to be of this world who can understand nothing beyond material things, which are the objects of sense in this world; as is the case with you, when, in your admiration of the sun and moon, you suppose all divine things to resemble them.
Deceivers, and being deceived, you call the author of this silly theory the Paraclete. But as you have no proof of his being the Paraclete, you have no reliable ground for the statement that the Gospel writings, which you receive only in part, are not of apostolic authorship. Thus your only remaining argument is, that these writings contain things disparaging to the glory of Christ; such as, that He was born of a virgin, that He was circumcised, that the customary sacrifice was offered for Him, that He was baptized, that He was tempted of the devil.
Source: Reply to Faustus the Manichaean (New Advent)