In New Testament scholarship, the Gospel of John is often viewed as a late document that adds little value to the historical Jesus. But the more I study John, the more I see the strong internal evidence that it was written by an eyewitness of Jesus’ life. Here are four of those reasons.

1. The author was very familiar with Jewish culture.

The author quotes various books in the Hebrew Old Testament such as Isaiah 6:10 (in 12:40) and Psalm 22:18 (in 19:24). He mentions Jewish feasts like Passover (2:13). In story of Lazarus, the author knows Jewish burial customs such as what kind of tomb Lazarus would be in along with how dead bodies were bound with linen (11:38-44). He gets archaeological details right like the Pool of Bethesda which was discovered in the 19th century. These details are easily explained if he was a Jew living during the time of Jesus. This by itself is by no means decisive, but it is a starting point.

2. The author seems to identify himself as the disciple “whom Jesus loved.”

Throughout the Gospel, the author refers to a disciple “whom Jesus loved.” Why does he only give a title like this to a single disciple? It seems obvious to me that it’s because he is referring to himself. In 21:20, the author says:

“Peter turned and saw the disciple whom Jesus loved following them, the one who also had leaned back against him during the supper and had said, ‘Lord, who is it that is going to betray you?'”

Here he repeats the comment that he made in 13:23. This comes just a few verses before the big reveal of his identity in verse 24 (more on that below).

Also, this Gospel records Jesus telling Mary to “behold her son” where Jesus is speaking of this same beloved disciple (19:26). Lastly, the author mentions that this disciple was with Peter when hearing the news of the empty tomb (20:2). If the author is the beloved disciple, then he can record these events because he was there.

3. The author has an insider’s knowledge of events. 

There are many details in John that seem to indicate the author had first-hand knowledge of certain events. For example, the author knows the times of certain events: “So they came and saw where he was staying, and they stayed with him that day, for it was about the tenth hour” (1:39). He also mentions the point when the disciples believed in Jesus (2:11).  The author was probably present in the boat when Jesus walked on the water because he knew that they had rowed the boat for “about three or four miles” (6:19).

The author is surprisingly specific with details that are not significant to the story, and I think it’s precisely because he remembers them happening!

4. The author claims to be an eyewitness.

The strongest piece of evidence is that the author claims to be an eyewitness. He says that he had physically seen Jesus while on the earth:

“And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth” (1:14).

In the middle of the crucifixion account, the author adds: “He who saw it has borne witness” (19:35).

Lastly, the author summarizes his work at the end of the Gospel:

“This is the disciple who is bearing witness about these things, and who has written these things, and we know that his testimony is true” (21:24).

Conclusion: The Author of John is an Eyewitness 

These four signs point strongly towards an eyewitness composing John’s Gospel. On top of this, an internal argument can be made to narrow down this beloved disciple to John, the son of Zebedee, as seen here. There is also external evidence that corroborates this view that I discuss here.

But even if we can’t know for sure if John the disciple wrote the Gospel, we can be confident that someone who walked with Jesus did.