The relatively small letter of Jude warns us against dangerous teachers entering in churches but who depart from biblical doctrine to exploit the credulity of their followers.
False prophets and teachers had already been foreseen by the Lord Jesus in Matthew 24:11 and later by Peter in his second letter in Chapter 2:1-2. Historians tell us that when the letter of Jude was written, the heresy of "Gnosticism" was being divulged, a system of religious philosophy whose adherents said they had perfect knowledge of the attributes of God (regardless of the Holy Scriptures), rejected the biblical doctrine of creation and denied the reality of the human body of Christ. Two of the results of the introduction of Gnosticism in the Christian environment at that time were irreverence and profligacy in the form of debauchery or immorality.
Addressing all of the "those who are called, sanctified by God the Father, and preserved in Jesus Christ" i.e. saved believers of all ages, Jude stated he felt the need to write "exhorting you to contend earnestly for the faith which was once for all delivered to the saints.” He wasn't referring to individual faith in Christ for salvation, but to the sum of the teachings given by the apostles and prophets that make up Christianity and distinguish it from Judaism and other religions. Let's note that this fundamental faith, which is the Gospel (this word is found 100 times in the New Testament), was delivered to the saints "once for all": it is permanent and unchangeable. It does not allow to consider as legitimate other gospels, whether in the form of new "revelations", papal bulls, messages of angels, or any other: "if anyone preaches any other gospel to you than what you have received, let him be accursed." (Galatians 1:9).
The exhortation is to contend for, and this means taking an active stance, unlike passivity. "To contend earnestly for the faith” means keeping faithfully and resolutely defending the fundamental and basic teachings of the Christian faith, the evangelical doctrine. Dangerous teachers penetrate in churches, and this is an indisputable reality common everywhere, and they will be successful if the church members remain passive. The consequences of this passivity will be serious and God's punishment will be severe. As examples, Jude cites the divine punishment that in the past times came on unbelievers and rebels of Israel, on the insolence of angels and also on the wickedness of the inhabitants of Sodom and Gomorrah.
Dangerous teachers, ungodly and apostate, are distinguished by four characteristics:
They are “dreamers" – their gospel is an illusion, far from the reality of the Scriptures "Let no one cheat you of your reward, taking delight in false humility and worship of angels, intruding into those things which he has not seen, vainly puffed up by his fleshly mind " (Colossians 2:18).
They defile their own body – they are immoral, they are contaminated both in their mind and their conscience, walking in the lust of uncleanness (Titus 2, 2 Peter 1:15, 2:10).
They reject authority - unruly, they reject the apostolic teaching, and will not recognize superior authority, whether in the family, in church or in the country, they are presumptuous and self-willed (2 Peter 2:10).
They speak evil of dignitaries, they speak evil of whatever they do not know, and this includes heavenly beings, possibly evil angels (2 Peter 2:11). We are informed that even Michael the Archangel did not dare to bring a reviling accusation against the devil (this incident is mentioned only here), but these supposed teachers scoff at what they do not understand and morally behave worse than animals. They are comparable to Cain, Balaam and Korah. Cain did not control his passions of jealousy and anger; Balaam, for love of money, disobeyed God and caused the people to sin grievously (Numbers 25:1-9; 31:8,16); Korah defamed Moses and Aaron and rebelled against them (Numbers 16).
We have the following seven parallels drawn from nature, illustrating the dangerous behaviour of teachers:
They are like "craggy rocks", dangerous for ships (verse 12, Young’s Literal Translation), or "spots and blemishes, carousing in their own deceptions while they feast with you" (2 Peter 2:13).
They are "gluttonous" feasting with the church (2 Peter 2:13).
They are "shepherding themselves" enticing unstable souls, having a heart exercised in covetousnesses (2 Peter 2:14).
They are like "clouds without water, by winds carried about", because they promise a lot but depart without giving any benefit.
They are “trees autumnal, without fruit, twice dead, rooted up" that are marked to be destroyed".
They are like "wild waves of a sea” that foul the beaches with the rubbish that they leave behind them: without control, raging, violent they only scatter noxious foam.
They are like "stars going astray", kept for the gloom of the darkness of the age. The stars going astray are comets, meteorites and other objects seen at night, that are useless to mariners because of their apparent instability, they glow for a little while and then disappear from view in the darkness of night. So neither can guidance be obtained from these dangerous teachers that glow for a little while in pulpits, platforms and televisions, and shortly afterwards disappear like fireworks.
Dangerous teachers were predicted by Enoch, of the seventh generation after Adam (Genesis 5:21 -24); He "walked habitually with God" and predicted the coming of the Lord to judge the wicked according to their deeds and their words. Note that this prophecy is not mentioned in Genesis, but (as the contention between Michael and Satan in v. 9) was informed by the Holy Spirit to Judas. In addition to the prophecy of Enoch, the apostles had already warned the church about the ungodly “teachers” before this letter of Jude. The words of Peter (2 Peter 33) are transcribed here and there is also reference to Romans 16:17-18 and 2nd. Timothy 3:1-8. Probably all the Apostles taught these things in their Ministry among the churches; see Acts 20.29-31.
These dangerous teachers, "ungodly shepherds", do not have the Holy Spirit (v 19), they never converted to Christ and were never born again. They are "sensual without spiritual insight" and cause divisions among Christians; they plant "churches" and "assemblies" that are their own and not of Christ.
Jude, in conclusion, indicates four ways for true believers to become immune to their influence and of protecting others from it: (vs. 20-23):
Building yourselves up on your most holy faith (v. 20). This is done by means of the study of the Word and by obedience to its teachings. Believers who neglect going to meetings for Bible study for the ministry of the Word are usually the first to be seduced by false teachers and those who cause divisions, because they are not founded or edified upon the doctrine of Christ.
Prayer. Here the Church gathered in prayer is meant; those who are regularly absent from these meetings are rarely believers given to private prayer at home! … However, the prayer "in the Holy Spirit" is actually the greatest protection against false teaching and sensuality.
Keeping in the love of God (v. 21). This love was shown in the Gospel of our salvation: "God so loved the world that He gave His only begotten Son" (John 3:16) - "by grace you have been saved through faith" (Ephesians 2:8). We expect the coming of the Lord and the perfection of our redemption (Romans 8:18,23). We are saved to holiness, and not to sin.
Having compassion for the weak and mistaken believers (vs. 22-23). Rather than censor them, let us to save them in the faith, praying for them, advising them with love. As for those that still seem to be lost, walking in sin (while calling themselves Christians, "more liberal"), we must have compassion for them, but watching for ourselves, separating ourselves entirely from evil.
The Epistle concludes with a remarkable peroration of praise to God "to Him who is able to keep you and present you”: to keep you from stumbling and to present you faultless before His throne. In verse 25, eternal praise (“from before the whole age, and now, and to all the ages” - Darby) is offered (“to the only God our Saviour”,"through Jesus Christ our Lord"- Darby), words that show us both the unity of God, as the equality of Jesus Christ with God the Father.
So ends this short, but important and solemn epistle. As we have seen (v. 4), profligates entered churches in apostolic times. During the centuries of the Middle Ages, the tares (Matthew 13:24-30) almost completely spoiled the morality and spirituality of Christianity. Nowadays, there are preachers and entire sects that deny "the faith once given to the saints", thus flouting the authority of the Bible and relaxing the Christian standard of morality and piety.
We must therefore be vigilant, loyal and active fighters in defense of the sanctity of the Gospel within our church, eliminating the manifestation of evil and taking care that dangerous teachers are not invited and heard inside it.