The author identifies himself as Jude (v. 1). The Greek is literally, Judas. Traditionally, English versions have used Jude to distinguish him from Judas who betrayed Jesus. Further, he identifies himself as the brother of James and bond-servant (Greek, doulos) of Jesus Christ. Jude is listed as the half-brother of Jesus in Matt. 13:55 and Mark 6:3. #2The NET Bible has this helpful note here:
Although Jude was half-brother of Jesus, he humbly associates himself with James, his full brother. By first calling himself a slave of Jesus Christ, it is evident that he wants no one to place stock in his physical connections. At the same time, he must identify himself further: since Jude was a common name in the first century (two of Jesus’ disciples were so named, including his betrayer), more information was needed, that is to say, brother of James.
The title in the Greek text is Iouda, an indeclinable form used for the Hebrew Judah and the Greek Judas.
Jude seems to write to no specific group of people. Rather the letter is simply addressed “to those who are called, wrapped in the love of God the Father and kept for Jesus Christ” (v. 1) and then later he addresses them as “beloved” or “dear friends” (v. 3).
Though the subject matter is very similar to 2 Peter, one of the chief differences between Jude and 2 Peter is that while Peter warned that “there shall be false teachers” (2:1), Jude states that “there are certain men who have secretly slipped in among you” (v. 4). Since 2 Peter anticipates the problem and Jude speaks of it as present, apparently Jude was written some time later than 2 Peter. If 2 Peter is dated about A.D. 66, then Jude might be placed around A.D. 70-80.
Jude intended to write about the common salvation, but because of the inroads of heresy and the danger threatening the church, he was compelled to write to encourage believers to contend earnestly for the faith against false teachings that were secretly being introduced in the churches. Evidently, definite advances were being made by an incipient form of Gnosticism—not ascetic, like that attacked by Paul in Colossians, but an antinomian form.
The Gnostics viewed everything material as evil and everything spiritual as good. They therefore cultivated their “spiritual” lives and allowed their flesh to do anything it liked, with the result that they were guilty of all kinds of lawlessness.
From this, two major purposes can be seen in Jude: (1) To condemn the practices of the ungodly libertines who were infesting the churches and corrupting believers, and (2) counsel believers to stand fast, continue to grow in faith while contending for the apostolic truth that had been handed down to the church.
The key idea or word is “contend for the faith.”
As with 2 and 3 John, since this book has only one chapter, this is not applicable.
Jude focuses our attention on the believer’s security in Christ (v. 24), on the eternal life He gives (v. 21), and on His sure coming again (v. 21). It is Jesus Christ our Lord who gives us access into God’s presence (v. 25).