Jude 1:4

For there are certain men crept in privily, even they who were of old written of beforehand unto this condemnation, ungodly men, turning the grace of our God unto lasciviousness, and denying our only Master and Lord, Jesus Christ.

There are certain men crept in privily ... These evil persons were the reasons for Jude's writing this letter. Just how he came to have this information is not specified; but presumably, he had received either some letter regarding it, or had been visited by one who knew the facts. It would appear that such people were apostate Christians, rather than rank outsiders. "In New Testament times, many of the enemies of the church were an emergence from within, rather than an intrusion from without."[15]

Whatever had been their beginnings, the evil men were at that time "ungodly," a favorite word with Jude. The Greek word [@asebeia] (ungodly) "is found 4 times in Romans 3 times in Timothy and Titus 1 time in 1 Peter 2 times in 2Peter, and 6 times in Jude."[16] "They had corrupted the concept of the grace of God so as to make it a cover for blatant immorality."[17] These heretics are here indicted in four charges: (1) they entered secretly; (2) they were prophetically consigned to doom; (3) they are ungodly; and (4) they deny Christ. As Wallace said, "To deny is positively to disbelieve what Christ testified about himself."[18]

Lasciviousness ... "This implies Gnostic antinomianism, which connotes sexual debauchery."[19] Such errors were clearly connected with the abuse of Paul's teachings regarding the grace of God; and the urgency with which Jude here undertook the refutation of it indicates that no great time had lapsed since Paul's letters of Romans, Galatians and Ephesians had appeared, thus corroborating the approximate date we have assigned to this letter.

Who were of old written of ... Macknight explained the meaning of this thus:

Jude means that the Scriptures relating the doom of Sodom, the punishment of angels, etc., whose sins were the same as those of these wicked men, were to be understood as examples of the punishment God would inflict upon them.[20]

[15] Alfred Plummer, op. cit., p. 509.

[16] Delbert R. Rose, op. cit., p. 432.

[17] Ibid.

[18] David H. Wallace, op. cit., p. 18.

[19] Ibid.

[20] James MacKnight, op. cit., p. 192.