II and III John have the same author. They speak the same language. They nearly agree in length and in epistolary form (address, introduction, conclusion). They carry at their head the same characteristic self-designation of the author, ho presbyteros...Now both Epistles are closely related to the Gospel of John and I John in language, style, and world view (summary of the material in R. H. Charles, The Revelation of St. John, ICC, I, XXXIV ff., XLI ff.). The emphasis upon the truth of the author's testimony in III 12 is similar to that in Jn. 19:35 and 21:24. III 11 expresses the characteristic Johannine view that one's fundamental being is to be inferred from the way one acts. II 4 ff. is full of parallels to conceptions from I John.

II and III John are either artificial creations prepared in conscious imitation of Johannine writing (so Dibelius, Jülicher-Fascher) - but their unpretentiousness militates against that - or they stem from the same author as I John and John.

As far as objections to the author of 2 and 3 John to have written the other Epistle and Gospel, Kümmel again writes,

Certain scholars, of course, have sought to ascribe II and III John to a different author from that of I John, because of particular differences in thought and language (e.g., Jülicher-Fascher, J. Jeremias, "Joh. Literarkritik," ThBl 20, 1941, 43, note 39, Bultmann). The following are not supposed to agree with Johannine thought: designation of a single false teacher as "the antichrist" (II 7); no "progressivist" (II 9) is to be received by the congregation (10 f.); Jesus Christ who "is come in the flesh" (I 4, 2) is called Jesus Christ who "comes in the flesh" (II 7); in contradiction to Jn. 1:18 and I 4:12a, III 11 says, "he who does evil has not seen God." These differences, however, are too trivial to be taken seriously.

These objections are in fact extremely insignificant:

• 2 John 1:7 is clear there are many who are "the" antichrist: a reflection of the ultimate man of lawlessness. If "houtos" is to be translated as "This [false teaching]" instead of "this one/person [who denies the incarnation]" then is an idea only to be the antichrist in any literal, non-metaphorical way?
• The idea of false teachers denying the incarnation is found in 1 John 4:1-6, 5:6-12, if that's the "progressivism" 2 John is allegedly unique in fighting.
• The supposed language difference in 1 Jn 4:2 and 2 Jn 1:7 is just absurd.
• 3 John 1:11 is not a doctrinal statement like Jn 1:18 and 1 Jn 4:12, but the same kind of theological qualification of religious life as Matt. 18:20 or 25:35 for example.

And the similarities are much more powerful. The word "antichrist" is found only in 1 John 2:18, 22, 4:3 and 2 John 1:7 in the NT. Both 1 John 4:1-6, 5:6-12 and 2 John 1:7 are fighting Docetism. The theme of the commandment of love in 1 John 2:3-11, 5:3 and 2 John 1:5-6 also strongly suggests the same author. Compare especially 1 Jn 2:7 and 2 Jn 1:5! So one can't really speak of a difference in thought or language either.

No personal references or appeal to the author as a witness is necessary: the errors do not require it. Ignatius fights Docetism in Epistle to the Trallians with no mention of an appearance to the Apostles as proof of Jesus' humanity and resurrection. And he only mentions the appearances twice in passing (cf. 1 Cor 15; apparently the type of proof depended on the author). The title "Presbyter" cannot prove this wasn't an apostle, since Papias specifically refers to five of the Twelve (John among them) as "presbyteroi". The author can easily dismiss the many false teachers with authority, but not force.

Date

The mention of deniers of Christ as coming in the flesh is usually taken to mean the docetic or Gnostic systems of the 2nd century. But there is no Gnosticism and the Docetism isn't advanced. Otherwise, the proof of the error of the heretics in 2 Jn 1:6 becomes illogical. The doctrine of Christ in 2 Jn 1:9 is certainly the commandments of morality and love in 1:5-6 and the deceivers preach doctrines of immorality (see discussion in 1 John). In any case, if we were dealing with advanced Docetism or Gnosticism, the arguments would be different as can be seen from Ignatius (epistle to the Trallians 10) with specific perpetrators mentioned (ep. Trallians 11), where the situation is far more acute (contrast with where some opponent is prominent like the Diotrephes crisis in 3 John). Thus, the primitiveness and overall facts allow us to say that II John does not deal with the heresies of the second century.

It seems the letter doesn't have the high theology and early Catholicism of 1 Clement (i.e. 2 John is primarily concerned with the commandment of love, whereas compare the topics in 1 Clement). Also, there is no appeal to the authority of bishops in fighting the heretics such as we see in Ignatius (ep. Trallians 5,7) and Clement (1 Clement 57), but knowing the truth through the Spirit and one's good works and love (1:4-6), so a date before 100 is possible. The second Christian generation is probably at least in the forefront seeing 1:5 ("..I am not writing you a new command but one we have had from the beginning...") and the problems of the Law before 60 appear to be solved seeing the overall atmosphere of concern only about righteousness (1:4-6, etc) unlike Paul.

The author addresses the church in a way that seems to imply he is addressing the congregation through the presbyters (1:4-6 which talk about the "children of the lady" i.e. congregations of the church, but why not address them directly as he does in 1:8-11, so clearly presupposes the presbyters to be firmly established as an authority; also see 1:13), whereas see Paul in addressing individuals in a congregation. But this hardly forces us to date it much after 60. Clement and Ignatius address their readers in much the same way Paul does, so then this (1:4-6) has to be regarded as the style of the author of II John. Appeals to commandments received from the Father (1:4-6) point away from early Catholicism, and thus an earlier date. In any case, the church authorities were apparently always known to be "shepherds of the flock" seeing Paul's address first to them in Philippians 1:1.

External Attestation

The scant external attestation is not a problem (no mention until the 3rd century). The letter is short and may have been doubted as apostolic, making its minimal material inapplicable to cite. And anything in it would've been covered by 1 John, which was accepted by the early 2nd century.