At the turn of this century, F. C. Conybeare, in a review of Alfred Loisy's Le quatrième évangile, wrote: ‘If Athanasius had not had the Fourth Gospel to draw texts from, Arius would never have been confuted.’ That is however only part of the truth, for it would also be true to say that if Arius had not had the Fourth Gospel to draw texts from, he would not have needed confuting. Without in any way diminishing the importance of other biblical writings in the development of the church's doctrine, it is St John's Gospel—and the First Epistle of St John—that brings into sharpest focus the problems which created doctrinal controversy in the early church and which indeed still perplex the church today.

Recent study has made it impossible to draw a hard and fast distinction between the Synoptic gospels as basically historical accounts of the life of Jesus and the Fourth Gospel as basically a theological interpretation of the significance of Jesus, a distinction which appears to have originated as early as the end of the second century when Clement of Alexandria wrote: ‘But last of all John, perceiving that the external facts (τὰ σωματικά) had been made plain in the gospel, composed a spiritual (πνευματικόν) gospel.’

The distinction was revived by Baur and the Tübingen school during the first half of the nineteenth century, and became axiomatic for nineteenth-century study of the gospels. In The Quest of the Historical Jesus, A. Schweitzer scarcely mentions the Fourth Gospel.