That this person was called John, therefore, and that this was the writing of a John, I do not deny. And I admit further, that it was also the work of some holy and inspired man. But I could not so easily admit that this was the apostle, the son of Zebedee, the brother of James, and the same person with him who wrote the Gospel which bears the title according to John, and the catholic epistle. But from the character of both, and the forms of expression, and the whole disposition and execution of the book, I draw the conclusion that the authorship is not his.
I. For the evangelist nowhere else subjoins his name, and he never proclaims himself either in the Gospel or in the epistle. … whether as of himself directly (in the first person), or as of another (in the third person). But the writer of the Revelation puts himself forward at once in the very beginning, for he says: “The Revelation of Jesus Christ, which He gave to him to show to His servants quickly; and He sent and signified it by His angel to His servant John, who bare record of the Word of God, and of his testimony, and of all things that he saw.” And then he writes also an epistle, in which he says: “John to the seven churches which are in Asia, grace be unto you, and peace.”
II. And from the ideas, and the expressions, and the collocation of the same, it may be very reasonably conjectured that this one is distinct from that. For the Gospel and the Epistle agree with each other, and both commence in the same way. … Thus the attentive reader will find the phrases, “the life,” “the light,” occurring often in both; and also such expressions as fleeing from darkness, holding the truth, grace, joy, the flesh and the blood of the Lord, the judgment, the remission of sins, the love of God toward us, the commandment of love on our side toward each other; as also, that we ought to keep all the commandments, the conviction of the world, of the devil, of Antichrist, the promise of the Holy Spirit, the adoption of God, the faith required of us in all things, the Father and the Son , named as such everywhere. And altogether, through their whole course, it will be evident that the Gospel and the Epistle are distinguished by one and the same character of writing. But the Revelation is totally different, and altogether distinct from this;
III. on the ground of difference in diction, it is possible to prove a distinction between the Gospel and the Epistle on the one hand, and the Revelation on the other. For the former are written not only without actual error as regards the Greek language, but also with the greatest elegance, both in their expressions and in their reasonings, and in the whole structure of their style. They are very far indeed from betraying any barbarism or solecism, or any sort of vulgarism, in their diction. … That the author of the latter, however, … I perceive that his dialect and language are not of the exact Greek type, and that he employs barbarous idioms, and in some places also solecisms.
— Dionysius: Extant Fragments ANF06