We know that his testimony is true
7 JUNE (Jn 21,20-25)
The Gospel is not based on fantasies and imaginations cleverly devised, developed by the mind of man. What Peter says of his faith in Christ Jesus can be applied to the whole Gospel: “We did not follow cleverly devised myths when we made known to you the power and coming of our Lord Jesus Christ, but we had been eyewitnesses of his majesty. For he received honor and glory from God the Father when that unique declaration came to him from the majestic glory, “This is my Son, my beloved, with whom I am well pleased.” We ourselves heard this voice come from heaven while we were with him on the holy mountain. Moreover, we possess the prophetic message that is altogether reliable. You will do well to be attentive to it, as to a lamp shining in a dark place, until day dawns and the morning star rises in your hearts. Know this first of all, that there is no prophecy of scripture that is a matter of personal interpretation, for no prophecy ever came through human will; but rather human beings moved by the holy Spirit spoke under the influence of God” (2Pt 1,16-21). John is a true eyewitness. He saw, he heard, he put everything in his heart and he wrote.
However, a truth must immediately be brought to light. John and the other Apostles neither see Christ with the eyes of their flesh, nor they understand hi with the light that comes out of their minds. We know from their own testimony that their eyes, ears and minds served nothing. The mystery of Jesus has remained veiled to them even after his glorious resurrection. They know the truth of Jesus not out of knowledge and human wisdom, but out of the intelligence of the Holy Spirit. This truth is affirmed with great incisiveness in the Gospel according to Luke: “He said to them, “These are my words that I spoke to you while I was still with you, that everything written about me in the law of Moses and in the prophets and psalms must be fulfilled.” Then he opened their minds to understand the scriptures. And he said to them, “Thus it is written that the Messiah would suffer and rise from the dead on the third day and that repentance, for the forgiveness of sins, would be preached in his name to all the nations, beginning from Jerusalem. You are witnesses of these things. And (behold) I am sending the promise of my Father upon you; but stay in the city until you are clothed with power from on high”” (Lk 24,44-49). Not only then, but every moment, every hour, every day the Lord has to open our minds, otherwise his mystery remains veiled.
John was able to narrate the life of Jesus according to the truth because he was assisted throughout by the Holy Spirit. For this reason, his testimony is true. It is the Spirit of the Lord the assurance of the truth of the Gospel. He is the guarantee not only in its writing, but also he must be guaranteed for its every interpretation. Whether it is written or it is visible to our eyes, we can understand the life of Jesus only with the wisdom, intelligence, light, knowledge and truth of the Holy Spirit. It is a veiled mystery and it will remain eternally veiled. Who can remove the veil is only He, the Spirit of the Lord. Who is in the Spirit, he understands. Who is without the Spirit, is blind.
Peter turned and saw the disciple following whom Jesus loved, the one who had also reclined upon his chest during the supper and had said, “Master, who is the one who will betray you?” When Peter saw him, he said to Jesus, “Lord, what about him?” Jesus said to him, “What if I want him to remain until I come? What concern is it of yours? You follow me.” So the word spread among the brothers that that disciple would not die. But Jesus had not told him that he would not die, just “What if I want him to remain until I come? (What concern is it of yours?)” It is this disciple who testifies to these things and has written them, and we know that his testimony is true. There are also many other things that Jesus did, but if these were to be described individually, I do not think the whole world would contain the books that would be written.
Is John immortal? No. The word of Jesus is clear. Every one of his apostles has his own particular mission to carry out. Everyone knows his. No one is allowed to know what God has written for the other. Even the Apostles of Jesus have a life surrounded by a great mystery. This mystery is known by the person and the Holy Spirit.
Virgin Mary, Mother of the Redemption, Angels and Saints help us know the mystery.