This is one of the most illuminating statements I’ve ever read about the uniqueness of the Gospel of John in relation to the others. C K Barrett:
“What John perceived [or, at least emphasized] with far greater clarity than any of his predecessors was that Jesus is the Gospel, and that the Gospel is Jesus. It was through the life, and especially through the death and resurrection, of Jesus that men had been admitted the blessings of the messianic kingdom, and the highest blessing of that kingdom was, as Paul had already seen, the life of communion with Christ himself: ‘for me, to live is Christ (Phil 1:21). That is, when the Gospel was offered to men it was Christ himself who was offered to them, and received by them” (Barrett, The Gospel According to St. John, 70).
This explains why John emphasizes that Jesus’ signs are, most essentially, revelations of the glory of Christ for the sake of belief (John 2:11). And that belief is, most essentially, a satisfaction in Christ himself (4:14; 7:37). And that the result of belief is eternal life which is, most essentially, knowing Christ himself (John 17:3).
John’s purpose is to show Jesus’ signs, that we might believe, that we might have life (John 20:30-31). It is Christ that the signs reveal, it is Christ that we delight in by faith, and it is Christ that we receive as our life.
Anything greater than this?