Woe unto them. It is a wonder that he inveighs against them so severely, when he had just said that it was not permitted to an angel to bring a railing accusation against Satan. But it was not his purpose to lay down a general rule. He only shewed briefly, by the example of Michael, how intolerable was their madness when they insolently reproached what God honored. It was certainly lawful for Michael to fulminate against Satan his final curse; and we see how vehemently the prophets threatened the ungodly; but when Michael forbore extreme severity (otherwise lawful), what madness was it to observe no moderation towards those excelling in glory? But when he pronounced woe on them, he did not so much imprecate evil on them, but rather reminded them what sort of end awaited them; and he did so, lest they should carry others with them to perdition. He says that they were the imitators of Cain, who being ungrateful to God and perverting his worship through an ungodly and wicked heart, forfeited his birthright. He says that they were deceived like Balaam by a reward, because they adulterated the doctrine of true religion for the sake of filthy lucre. But the metaphor he uses, expresses something more; for he says that they overflowed, even because their excess was like overflowing water. He says in the third place, that they imitated the contradiction of Core, because they disturbed the order and quietness of the church.

Woe unto them! - See Matthew 11:21.
For they have gone in the way of Cain - Genesis 4:5-12. That is, they have evinced disobedience and rebellion as he did; they have shown that they are proud, corrupt, and wicked. The apostle does not specify the points in which they had imitated the example of Cain, but it was probably in such things as these - pride, haughtiness, the hatred of religion, restlessness under the restraints of virtue, envy that others were more favored, and a spirit of hatred of the brethren (compare 1-John 3:15) which would lead to murder.
And ran greedily after the error of Balaam for reward - The word rendered "ran greedily" - (ἐξεχύθησαν exechuthēsan,) from ἐκχέω ekcheō - means to pour out; and then, when spoken of persons, that they are "poured out," or that they "rush tumultuously" on an object, that is, that they give themselves up to anything. The idea here is, that all restraint was relaxed, and that they rushed on tumultuously to any course of life that promised gain. See the notes at 2-Peter 2:15.
And perished - They perish, or they will perish. The result is so certain, that the apostle speaks of it as if it were already done. The thought, seems to have lain in his mind in this manner: he thinks of them as having the same character as Korah, and then at once thinks of them as destroyed in the same manner, or as if it were already done. They are "identified" with him in their character and doom. The word rendered "perish" (ἀπόλλυμι apollumi) is often used to denote future punishment, Matthew 10:28, Matthew 10:39; Matthew 18:14; Mark 1:24; Luke 13:3, Luke 13:5; John 3:15-16; John 10:28; 2-Thessalonians 2:10; 2-Peter 3:9.
In the gainsaying of Core - Of Korah, Numbers. 16:1-30. The word "gainsaying" here means properly contradiction, or speaking against; then controversy, question, strife; then contumely, reproach, or rebellion. The idea here seems to be, that they were guilty of insubordination; of possessing a restless and dissatisfied spirit; of a desire to rule, etc.

They have gone in the way of Cain - They are haters of their brethren, and they that are such are murderers; and by their false doctrine they corrupt and destroy the souls of the people.
The error of Balaam - For the sake of gain they corrupt the word of God and refine away its meaning, and let it down so as to suit the passions of the profligate. This was literally true of the Nicolaitans, who taught most impure doctrines, and followed the most lascivious practices.
Gainsaying of Core - See the account of the rebellion of Korah, Dathan, and Abiram, and their company, in Numbers. 22. It appears that these persons opposed the authority of the apostles of our Lord, as Korah and his associates did that of Moses and Aaron; and St. Jude predicts them a similar punishment. In this verse he accuses them of murder, covetousness, and rebellion against the authority of God.

(9) Woe unto them! for they have gone in the way of Cain, and ran greedily after the error of Balaam for reward, and perished in the gainsaying of Core.
(9) He foretells their destruction, because they resemble or proclaim Cain's shameless malice, Balaam's filthy covetousness, and to be short, Core's seditious and ambitious head.

Woe unto them,.... This may be considered as a commiseration of their case, or as a denunciation of deserved punishment, or as a prediction of what would befall them. The Arabic version prefaces these words with an address to the saints, "O my beloved": that what was about to be said might be attended to, as a caution and instruction to them,
For they have gone in the way of Cain; which was a way of envy, for Cain envied the acceptance of his brother's gift, and that notice which the Lord took of him; so these men envied the gifts bestowed on Christ's faithful ministers, and the success that attended their labours, and the honour that was put upon them by Christ, and that was given them by the churches; which shows, that they were destitute of grace, and particularly of the grace of charity, or love, which envies not, and that they were in an unregenerate estate, and upon the brink of ruin and destruction. Moreover, the way of Cain was a way of hatred, and murder of his brother, which his envy led him to; so these men hated the brethren, persecuted them unto death, as well as were guilty of the murder of the souls of men, by their false doctrine: to which may be added, as another of Cain's ways, in consequence of the former, absence from the presence of God, or the place of his worship; so these men separated themselves, and went out from the churches, forsook the assembling together with them, and so might expect Cain's punishment, to be driven from the face of God; yea, to be bid go as cursed into everlasting burnings:
and ran greedily after the error of Balaam for reward; Balaam's error, which he himself was guilty of, was covetousness, or an immoderate love of money, 2-Peter 2:15; which, as it is the root of all evil, is the bane of religion, and the source of heresy, and what the false teachers were greatly addicted to; and where it prevails, it is insatiable, and not to be checked and stopped, as in these men; and is a damnable sin, and excludes from the kingdom of heaven, as well as is dishonourable to religion; hence such particular notice is taken of it, lest it be found in a minister of the word: this character exactly agrees with the followers of Simon Magus. The error which Balaam led others into, was both idolatry and adultery, Revelation 2:14, which these false teachers were both guilty of themselves, and taught others, and indulged them therein; and which both teachers and people ran greedily after. Balaam is one of the four private persons, who, according to the Jews, shall have no part or portion in the world to come (w),
And perished in the gainsaying of Core: the same with Korah, Numbers 16:1. The Septuagint there call him Core, and so does Philo the Jew (x), as the apostle does here, and by Josephus he is called (y) "Cores": now the gainsaying or contradiction of these men was like Korah's; as his was against Moses, the ruler of the people, so theirs was against magistracy, Jde 1:8; which was gainsaying God's own ordinance, and a contradiction of that which is for the good of men; the ground of which contradiction was love of liberty, and their own lusts; and, generally speaking, men perish in their factions and rebellions against good and lawful magistrates: also, as Korah gainsayed Aaron, the priest of the Lord, so these men contradicted and opposed the ministers of Christ, whom they would have thrust out in order to put in themselves, and whose persons they reviled, and contradicted their doctrines, which to do is of dangerous consequence; and they might be said to perish in his gainsaying, as a type and example of their destruction, which would be swift and sudden, as his was; and to denote the certainty of it. So the Jews (z) say of Korah and his company, that they shall never ascend, or rise up and stand in judgment, and that they shall have no part or portion in the world to come (a),
(w) Misn. Sanhedrin, c. 11. sect. 2. (x) De Profugis, p. 471. (y) Antiqu. l. 4. c. 2. sect. 2. (z) Misn. Sanhedrin, ib. sect. 2. Yalkut Simeoni, par. 2. fol. 89. 3. Sanhed. ib. sect. 3. (a) T. Hieros. Sanhedrin, fol. 29. 3.

Woe--See on 2-Peter 2:14, "cursed children."
Cain--the murderer: the root of whose sin was hatred and envy of the godly, as it is the sin of these seducers.
ran greedily--literally, "have been poured forth" like a torrent that has burst its banks. Reckless of what it costs, the loss of God's favor and heaven, on they rush after gain like Balaam.
perished in the gainsaying of Core--(compare Note, see on Jde 1:12). When we read of Korah perishing by gainsaying, we read virtually also of these perishing in like manner through the same: for the same seed bears the same harvest.

Woe unto them! The denunciation of woes, common in the Lord's ministry, is only found here in all the rest of the New Testament.
Gone in the way of Cain. Living selfish lives, full of hate.
After the error of Balaam. Like Balaam trying to make a gain of godliness.
Perished in the gainsaying of Core. Like Balaam they are false prophets. Like Korah, who profanely thrust himself into the priesthood and perished, they intrude irreverently into holy places.
These are spots in your feasts of charity. See notes on 2-Peter 2:13. They engaged in revelings at the Agape, the love feasts.
Clouds they are without water. Rainless clouds.
Trees . . . without fruit. Fruitless, barren.
Twice dead. Doubly dead, hence, no hope of fruit.
Raging waves of the sea. Roaring and foaming like the sea waves.
Wandering stars. Stars not fixed in their places, but shooting like meteors, and then going out. "Shooting stars" is not far from the idea.
To whom is reserved, etc. As the shooting stars go out in darkness, so these will pass into eternal darkness.

Woe unto them - Of all the apostles St. Jude alone, and that in this single place, denounces a woe. St. Peter, to the same effect, pronounces them "cursed children." For they have gone in the way of Cain - The murderer. And ran greedily - Literally, have been poured out, like a torrent without banks. After the error of Balaam - The covetous false prophet. And perished in the gainsaying of Korah - Vengeance has overtaken them as it did Korah, rising up against those whom God had sent.