John 21:24-25 is clearly that John was not the author of this passage especially when words like we are used.
Johns gospel is the last Gospels around 90-120 years and its primary purpose is to show the deity of Christ. Note that the first mention of the bible written by a disciple was Irenaeus in the year 180.
There are a number of issues regarding Irenaeus which I will not go in to detail, but in summary he had a number of issues with the early church fathers & early Christian groups based on his book "Against Heresies". None of the early Christians knew who he was and the original transcript was not available only a ‘Latin’ copy without no idea who translated it.
He relies mainly on the Gospel of John which is referred to as the ‘spiritual Gospel’.
The American Bishop John Shelby Spong said: intensive five-year-long study of John’s Gospel - There is probably not a single word attributed to Jesus in this book that the Jesus of history actually spoke
Was this just a 'post scriptum' by other scholars & is the rest by John valid?
The discovery and publication in the 1930s of a papyrus fragments known as P52 was the earliest physical evidence that exists for the Gospel of John. Palaeographic dating has been used and recent examination say it could date around 200 years after Jesus. Palaeography is not the most effective method for dating texts.
Gospel does not emerge clearly in the historical record until the end of the 2nd century. Justin Martyr (100 – 165 CE) was an early Christian apologist and is regarded as the foremost interpreter of the theory of the Logos, a theology that is also found in John’s Gospel.
In the 2nd century Justin Martyr advocated a logos Christology without citing John’s Gospel explicitly. Such an omission by Justin would seem strange if the Gospel of John had already been written and was in circulation.
Another important factor is bishop Polycarp according to church history he was a student of John the Apostle, even ordained by him. The letter of Polycarp to the Philippians, generally thought to be from around 135 CE, never quotes from John, and never even alludes to it. Yet other New Testament writings are quoted abundantly in his letter. Even though he quotes the Gospels of Mark, Matthew and Luke, not one quote from John. This is incredible, the one person whose Gospel he should have written about and he didn’t.
There’s really no explicit attestation for John until the bishop Irenaeus, late in the 2nd century. Therefore, making it impossible that the disciple of Jesus was the author.
Another big problem with the Gospel of John
The Gospels of Mark, Matthew and Luke include many of the same stories, often in the same sequence, and similar wording. Unlike, John, 90% of its material cannot be found in the Synoptics. Here are some examples
i. The spear piercing the side of Jesus.
“Instead, one of the soldiers pierced Jesus’ side with a spear, bringing a sudden flow of blood and water.” [John 19:34]
So Judas came to the garden, guiding a detachment of soldiers and some officials from the chief priests and the Pharisees. They were carrying torches, lanterns and weapons.
Jesus, knowing all that was going to happen to him, went out and asked them, “Who is it you want?”
“Jesus of Nazareth,” they replied.
“I am he,” Jesus said. (And Judas the traitor was standing there with them.) When Jesus said, “I am he,” they drew back and fell to the ground.
[John 18:3-6]
It is strange to think that the authors of the Synoptic would not have been aware of incidents such as the spear piercing the side of Jesus and the soldiers prostrating to him in the Garden of Gethsemane, had they really taken place. It is even more inconceivable that they would have intentionally omitted such remarkable accounts from the Synoptic.
John does not mention the story of Christ's ascension – which Luke & Mark do - Luke 24:51-52 / Mark 16:19-20.
miracle of reviving the girl who had died Mark 5:35 / Luke 8:49-55 / Matthew 9:23-25
transfiguration incident - Matthew 17:1-5 / Luke 9:28-35
Although John the son of Zebedee was an eyewitness to that unique miracle.
does not mention his first meeting with Jesus
John also contradicts the others
Here is Matthew’s account of the tomb visit:
“Now after the Sabbath, toward the dawn of the first day of the week, Mary Magdalene and the other Mary went to see the tomb. And behold, there was a great earthquake, for an angel of the Lord descended from heaven and came and rolled back the stone and sat on it” [Matthew 28:1-2]
But the angel said to the women, “Do not be afraid, for I know that you seek Jesus who was crucified. He is not here, for he has risen, as he said. Come, see the place where he lay. Then go quickly and tell his disciples that he has risen from the dead, and behold, he is going before you to Galilee; there you will see him. See, I have told you” [Matthew 28:5-7]
So they departed quickly from the tomb with fear and great joy, and ran to tell his disciples. And behold, Jesus met them and said, “Greetings!” And they came up and took hold of his feet and worshiped him. [Matthew 28:8-9]
So, in Matthew’s account Mary Magdalene is presented as having seen an angel at the tomb and heard the angel announce the resurrection of Jesus. After which she actually encountered Jesus as she was running away from the tomb in order to inform the disciples about what had happened.
Now here is John’s account of the tomb visit:
Now on the first day of the week Mary Magdalene came to the tomb early, while it was still dark, and saw that the stone had been taken away from the tomb. So, she ran and went to Simon, Peter and the other disciple, the one whom Jesus loved, and said to them, “They have taken the Lord out of the tomb, and we do not know where they have laid him” [John 20:1-2]
In John’s Gospel, however, Mary Magdalene is presented as having found the tomb empty, after which she ran to the disciples and told them that the body of Jesus had been stolen.
Last Supper
And on the first day of Unleavened Bread, when they sacrificed the Passover lamb, his disciples said to him, “Where will you have us go and prepare for you to eat the Passover?” And he sent two of his disciples and said to them, “Go into the city, and a man carrying a jar of water will meet you. Follow him, and wherever he enters, say to the master of the house, ‘The Teacher says, where is my guest room, where I may eat the Passover with my disciples?’ And he will show you a large upper room furnished and ready; there prepare for us.” And the disciples set out and went to the city and found it just as he had told them, and they prepared the Passover. And when it was evening, he came with the twelve. And as they were reclining at table and eating, Jesus said, “Truly, I say to you, one of you will betray me, one who is eating with me” [Mark 14:12-18]
So, Jesus sent Peter and John, saying, “Go and prepare the Passover for us, that we may eat it” [Luke 22:8]
John
“It was just before the Passover Festival. Jesus knew that the hour had come for him to leave this world and go to the Father. Having loved his own who were in the world, he loved them to the end. The evening meal was in progress…” [John 13:1-2]
John implies no last supper.
A few more examples:
John 8:2-11 is the story of a woman that is about to be stoned on the accusation of adultery.
The next day John saw Jesus coming toward him and said, “Look, the Lamb of God, who takes away the sin of the world!” [John 1:29] No one else mentions 'the lamb'
Turning water into wine
“Jesus performed many other signs in the presence of his disciples, which are not recorded in this book. But these are written that you may believe that Jesus is the Messiah, the Son of God, and that by believing you may have life in his name” [John 20:30-31]
Jesus' encounter with Simon (Peter), Andrew, James, and John different to the other Gospels
Not mentioning the names of Jesus' disciples apart from Andrew, Peter & Philip – others mention in details
does not mention his mother Salome who went to anoint Jesus with sweet spices – yet Mark 16:1-7 does
Not mentioning the genealogy of Jesus and his miraculous birth from a virgin and the incident of Temptation of Christ by Satan mentioned by the others
Not mentioning the miracle of Peter walking on water
Thomas meeting with Jesus
Again, only John mentions this event, although all the disciples were present.
John 20: 24 But Thomas, one of the twelve, called Didymus, was not with them when Jesus came.
YET
Luke 24: 33 And they rose up that very hour, and returned to Jerusalem, and found the eleven gathered together, and them that were with them,
There were only eleven by then as Judas had killed himself – so Thomas must have been at the first meeting of the eleven
Some say the eleven is used as a general term to refer to the apostles, however there is no supporting passage to imply this.
Conclusion:
- Uneducated: When they saw the courage of Peter and John and realized that they were unschooled, ordinary men, they were astonished and they took note that these men had been with Jesus. [Acts 4:13]
- The others have many of the same stories but not John
- A lot is written in the third person such as; 21:24 - “This is the disciple who testifies to these things and who wrote them down. We know that his testimony is true.” One of them, the disciple whom Jesus loved, was reclining next to him. [John 13:23]
- The Synoptics paint the picture of Jesus that is reluctant to be crucified. For example, they all mention Jesus’ begging God to be saved from death when he is in the Garden of Gethsemane. Luke even has Jesus sweating drops of blood just before his arrest. All of this is in stark contrast to John, who portrays Jesus as willingly handing himself over to the authorities - John 18:3-6.
- John, 1:1-18 - The passage is written in a highly poetic style that’s not found in the rest of the Gospel of John. These verses also contain key concepts not found in the rest of the Gospel, such as Jesus being “the Word” made flesh. Jesus is called the “logos” twice in the prologue and never anywhere else in the Gospel of John (or even the entire New Testament for that matter).
Clearly, the author of John was not the disciple of Jesus and the writing come much later.