Dominum et Vivificantem §5

⁵ In transmitting the Good News, the Apostles will be in a special way associated with the Holy Spirit. This is how Jesus goes on: "When the Counselor comes, whom I shall send to you from the Father, even the Spirit of truth, who proceeds from the Father, he will bear witness to me; and you also are witnesses, because you have been with me from the beginning." Apostles were the direct eyewitnesses. They "have heard" and "have seen with their own eyes," "have looked upon" and even "touched with their hands" Christ, as the evangelist John says in another passage. This human, first-hand and "historical" witness to Christ is linked to the witness of the Holy Spirit: "He will bear witness to me." In the witness of the Spirit of truth, the human testimony of the Apostles will find its strongest support. And subsequently it will also find therein the hidden foundation of its continuation among the generations of Christ's disciples and believers who succeed one another down through the ages. The supreme and most complete revelation of God to humanity is Jesus Christ himself, and the witness of the Spirit inspires, guarantees and convalidates the faithful transmission of this revelation in the preaching and writing of the Apostles, while the witness of the Apostles ensures its human expression in the Church and in the history of humanity.