Exposition of the Old and New Testament, by John Gill, [1746-63], at sacred-texts.com
That this epistle was written by Jude, one of the twelve apostles of Christ, and not by Jude the fifteenth bishop of Jerusalem, who lived in the time of Trojan, a little before Bar Cocab, the false Messiah, as Grotius thought, is evident from his being called, in the epistle itself, the brother of James, and which is confirmed by all copies; and its agreement with the second epistle of Peter shows it to have been written about the same time, and upon the same occasion. As to Jude's not calling himself an apostle, but a servant of Jesus Christ, it may be observed, that the latter is much the same with the former, and the Apostle Paul sometimes uses them both, as in Rom 1:1, Tit 1:1, and sometimes neither, as Th1 1:1, and sometimes only servant, as Jude does here, Php 1:1, though in some copies of the title of this epistle he is called "Jude the Apostle"; and as to Jude's making mention of the apostles as if he was later than they, and not of their number, Jde 1:17, it may be returned for answer to it, that the Apostle Peter expresses himself much in the same manner, Pe2 3:2, where some copies, instead of "us the apostles", read "your apostles", Pe2 3:2; moreover, Jude seems to cite a passage out of Peter, as Peter in the same chapter cites the Apostle Paul, which only shows agreement in their doctrine and writing; and at most it only follows from hence, that Jude wrote after some of the apostles, as Paul and Peter, who had foretold there would be mockers in the last time; and that Jude had lived to be a witness of the truth of what they had said; nor does he exclude himself from their number. And that this epistle is a genuine one appears from the majesty of its style, the truth of doctrine contained in it, and its agreement with the second epistle of Peter, and from the early reception of it in the churches. Eusebius (a) says, it was reckoned among the seven catholic epistles, and was published in most churches; though he observes, that many of the ancients make no mention of it: but certain it is, that several of the ancient writers before him do make mention of it, and cite it as genuine, as Clemens Alexandrinus (b), Tertullian (c), and Origen (d): and as for the prophecy of Enoch, cited in this epistle, it is not taken out of an apocryphal book, that bears that name, for the apostle makes no mention of any writing of his, but of a prophecy; and had he cited it out of that book, as it was truth, it can no more prejudice the authority of this epistle, than the citations made by the Apostle Paul out of the Heathen poets can affect his epistles: and whereas there is an account also given in this epistle of a dispute about the body of Moses, nowhere else to be met with, supposing it to be understood of his real body, of which Jde 1:9; this can be no more an objection to the genuineness of this epistle, than the mention of Jannes and Jambres, who withstood Moses, by the Apostle Paul, Ti2 3:8, is an objection to an epistle of his, whose names are not to be met with in other parts of Scripture; but were what were known by tradition, as might be the case here. The epistle is called "catholic", or "general", because it is not written to any particular person or church, but to the saints in general, and it may be to the same persons that Peter wrote his; see Pe1 1:1, and who seem to be chiefly the believing Jews; see Jde 1:5, though the Syriac version of Jde 1:1 reads, "Jude, a servant of Jesus Christ"--ammel, "to the nations", or "Gentiles, called", &c. the design of the epistle to both is to exhort them to continue in the faith, and contend for it; and to describe false teachers, to point out their principles, practices, and dreadful end, that so they might shun and avoid them.
(a) Hist. Eccles. l. 2. c. 23. (b) Paedagog. l. 3. c. 8. p. 239. & Stromat. l. 3. p. 431. (c) De Cultu Foemin. l. 1. c. 3. (d) In Josh. Homil. 7. fol. 156. E. & Comment, in Matth. p. 223. Ed. Huet.