Jude's Epistle has many Old Testament examples of apostasy to remind his audience of the consequences of turning the grace of God into lascivousness. The first example he gives is in verse 5 which is probably a reference to Israel's unbelief at Kadesh (Num. 13-14). There, spies from each of the twelve tribes of Israel gave an evil report, that the land was hostile to its inhabitants, and that giants dwelt in the land. The example of apostasy is found in their desire to appoint a captain and return to Egypt. The consequence of their unbelief was that the Lord destroyed them.
Israel's other instance of unbelief and rebellion also serves as an example of widespread departure from the faith when they were at Horeb in Exodus 32. However, that moment in Israel's history was likely not what Jude was referring to here as There, we read of how the camp of Israel grew restless waiting for Moses, so they went to Aaron and fashioned a golden calf from the bracelets and jewelry they took as a spoil on their departure from Egypt. When Moses came down from the mountain, and saw the debauchery that took place, he asked who would come to the LORD's side. All the tribe of Levi came and were commanded to kill their brethren. In that day three thousand souls who were saved out of the land of Egypt perished for their unbelief. The psalmist declares of this incident that "They changed their Glory into the likeness of an ox that eats grass." This idol was who they gratified their flesh after in the name of worship. The idol, being made of the gold they took out of Egypt is a stunning picture of turning the grace of our God into lasciviousness and denying our Lord Jesus Christ.
The desire to create an idol started nearly immediately from the time they left Egypt, for it was an attempt to re-create some of the things they had in Egypt which they missed. You will remember the murmurings of the Israelites, desiring food and water, and ironically, to be buried in Egypt rather than journey through the wilderness to get to the Promised Land! Many believers today miss the world that they have been brought out of so much that they take their christian liberty, a blessing or spoil of victory, and use it to pervert the grace of Jesus Christ. I am reminded of christian leaders who make a case for the believer's liberty to engage in fleshly practices such as smoking or using unedifying language.
It has been commonly understood by many godly commentators that apostasy is an irremmediable sin. The basis for this teaching is found in passages such as Heb. 6:4-6; 2 Peter 2:17,21; Jude 12,13 and 19; and Rev. 3:14-16. While some look to it as proof that apostasy is irremmediable, other teachers look to it as proof that a believer can backslide so far they can never come back to full fellowship. Both views are extreme and a warning ought to be given to tread softly where one is unsure of how to interpret a passage. It can be difficult to know where to draw the line between an apostate and a backslidden believer. The backslider may lose fellowship with Christ for a period through sin, but an apostate never had fellowship, and never will. The backslider, like some of the saints at Corinth, usually experience some sort of chastisement or discipline, are delivered unto Satan for destruction of the flesh that the spirit may be saved (1 Corinthians 5:5). But for the apostate: the mist of darkness is reserved forever (2 Peter 2:17). The carnal believer being sealed by the Spirit, may grieve Him nevertheless (Ephesians 4:30). The apostate is devoid of the Spirit (Jude 1:19).
Before moving on, I want to clarify my position that apostasy is a sin that can not be committed by a true believer. A true believer can fall into sinful, carnal living as the Corinthian believers did, but if he denies the Person and work of the Lord Jesus Christ, he never believed in the first place. If a believer does start living a sinful lifestyle, then there he or she will surely experience chastening in their life to bring them to repentance. The author of Hebrews reminds us in the twelfth chapter: "If ye endure chastening, God dealeth with you as with sons; for what son is he whom the father chasteneth not? But if ye be without chastisement, whereof all are partakers, then are ye bastards, and not sons." (Heb. 12:7-8). Chastisement is a proof of sonship, that we have been adopted into the family of God, along with the presence of the indwelling Spirit (Rom. 8:16). An apostate has never experienced God's chastisement, nor has he the Spirit of God bearing witness with our spirit.
Wherefore the rather, brethren, give diligence to make your calling and election sure: for if ye do these things, ye shall never fall:
2 Peter 2:10