The author

Traditionally the author is identified as Jude, the brother of James and possibly a kinsman of Jesus.

Critique

This epistle is questioned because it quotes from apocryphal books like the Assumption of Moses and 1 Enoch which are not considered to be authoritative by most Christians.

Jude 1:9

Three early church fathers, Clement of Alexandria (A.D. 155–220), Origen (A.D. 185—254), and Didymus of Alexandria (A.D. 309/314–398), state that Jude 9 and the Assumption of Moses refer to the same event, however the existing manuscript of the Assumption of Moses does not contain a passage similar to Jude 1:9

Jude 1:14-15

Now Enoch, the seventh from Adam, prophesied about these men also, saying,

“Behold, the Lord comes with ten thousands of His saints, to execute judgment on all, to convict all who are ungodly among them of all their ungodly deeds which they have committed in an ungodly way, and of all the harsh things which ungodly sinners have spoken against Him.”

-- Jude 1:14-15 (NKJV)

Quotes from:

Behold, he comes with the myriads of his holy ones, to execute judgment on all, and to destroy all the wicked, and to convict all flesh for all the wicked deeds that they have done, and the proud and hard words that wicked sinners spoke against him. -- 1 Enoch 1:9