The letter of Jude is a brief and powerful letter. If you read the letter, you notice the drive of a prophet. God’s Spirit has used Jude to describe in the dynamic, energetic language of the prophets the evil in professing Christianity and the judgment on it at the coming of the Lord Jesus.
The picture presented to you here of professing Christianity is not a picture that makes you cheerful, but it is reality. If that reality were withheld from you, you would miss the necessary warnings that should help you recognize the attacks made on God’s truth. At the same time Jude encourages you. He points at the unfaltering faithfulness and omnipotence of God and the Lord Jesus for those who are willing to hold on to the truth which was once for all handed down to them and to defend it against the attacks.
If you read this letter and compare it with chapter 2 of the second letter of Peter, you will see that certain topics are mentioned in both letters. These same topics, however, are presented from a different point of view. Peter addresses Jewish Christians and speaks about sin and unrighteousness. Jude addresses all Christians and speaks about the apostasy of the Christian truth, the abandonment of the most holy faith.