Dating the gospels
Unlike the other gospels, John the apostle is never named in the Gospel of John, though his name seems to be deliberately self-obscured by calling himself "another disciple" or the "disciple that Jesus loved" (John , -16, -27, 20:2-4, 20:8, 21:7, , -24).The "we" in John indicates that the author, along with the other apostles, were eyewitnesses of Jesus.John says: "This is the disciple who is testifying to these things and wrote these things, and we know that his testimony is true." The "he" in this verse at the end of the book is probably John, and the "we" is almost surely the Christian community working with him to put the book into its final form. Also, one major point should be made about all the Johannine literature: it is very easy to read, much more so than anything by Peter, Paul, Luke or Hebrews (Ask a beginning Greek student!) This is understandable when one considers that Greek was not John's first language.2 John says Though I have many things to write to you, I do not want to do so with paper and ink; but I hope to come to you and speak face to face, while 3 John 13-14 has the remarkably similar I had many things to write to you, but I am not willing to write them to you with pen and ink; but I hope to see you shortly, and we will speak face to face.
Holding John the son of Zebedee to be the author of Revelation are the second century church fathers Justin Martyr and Irenaeus, along with third century fathers Clement of Alexandria, Tertullian of Carthage, Origen of Alexandria, and Hippolytus of Rome.
Both 1 and 2 John speak of a new commandment (1 John 2:8, 2 John 5) of love.
Truth is a key concept in all three (1 John 1:6, 1:8, , , 4:6, 5:6; 2 John 1, 2, 4; 3 John 1, 3, 4, 8, 12).
Only Rev 1:7 and John say Jesus was pierced." The picture of Christ as a lamb is also prominent in both books. John, who bore record of the word of God and the testimony of Jesus Christ, and of all things that he saw", could be read as saying that the author of this book previously wrote the gospel as well.
Some scholars have argued for different authors for John and Revelation because of differences in how the Greek language is used in the two books.