It seems that there is no real reason to doubt that the author was Jude, the brother of Jesus. In the opening lines, the author identifies himself as 'Jude...the brother of James,' and to the best knowledge of modern scholarship, there was no other James that would be assumed apart from James, the brother of Jesus and the leader of the Church in Jerusalem until his death.
It is often questioned why, if this were the case, Jude did not open with 'Jude, a brother of Jesus'. James similarly, in the opening of his letter, neglects to mention any blood relationship with our Lord. We can take this to mean that both James and Jude, in true Christian humility, preferred to view themselves as servants of Jesus (Jas. 1:1 & Jude 1:1), rather than his brothers.
There was a Jude among the apostles, but the possibility of that Jude being the author is negated by his introduction, seeking recognition by his brother James. If the author were an apostle, that would have been recognition enough for the letter to be viewed as authoritative in itself. Also, verse 17 seems to be written from the perspective of someone who is not an apostle.
Although some modern scholars claim this letter to be pseudepigraphical (written by someone else under the name of a well-known author), there is no explanation why, if this were the case, the real author chose Jude. From the surviving records, there is no evidence to suggest that Jude was particularly authoritative or well known in the early Church. It would have made more sense for the author to choose a better known Christian leader than Jude in order to impose authority on their letter.
However, it is natural to assume, and there is evidence to suggest, that the brothers of Jesus did teach concerning Him, and would have been viewed by others as in some way authoritative-by-blood - or at least respected because of their kinship with Jesus. There is the possibility that the letter was written by Jude to parts of the Church he had preached to, and therefore recognised him as authoritative. This, and the acceptance of the author being the brother of James and therefore the brother of Jesus probably accounted for the wide acceptance the letter received in the early Church.
Overall, there is no reason to doubt the claims of the letter, that it was written by Jude, the brother of James, and therefore the brother of Jesus.
It is very hard to date this letter as there is nothing within the content of the epistle that points towards a certain date. Taking other factors into consideration, those who view the author to be Jude the brother of Jesus date this between 65 and 100 AD, obviously noting that Jude would have been about 100 years old himself to have written it in 100 AD. Others who view the letter as pseudepigraphical date the letter somewhere in the late first, or early second century.
- 1-2 Jude, a servant of Jesus and brother of James, to those who have been called: Mercy, peace and love be yours in abundance.
- 3-16 I felt I had to write and urge you to contend for the faith, for certain godless men have slipped in among you, who change the grace of God into a license for immorality. Their destruction was written about long ago, and will be similar to the destruction of the rebellious angels, those who were delivered by God out of Egypt but did not believe, and the people of Sodom and Gomorrah. These men think only of themselves and are a blemish at your feasts.
- 17-22 But remember, the apostles of our Lord foretold: "In the last times there will be scoffers who follow their own ungodly desires". But you, dear friends, build yourselves up in your faith and pray in the Holy Spirit. Be merciful to others, hating even the clothing stained by corrupted flesh.
- 23-25 To the God who has truly saved us, be glory, power and authority forever! Amen.