For they have gone in the way of Cain. Ge 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 favoured, and a spirit of hatred of the brethren (comp.1 Jo 3:15) which would lead to murder.

And ran greedily after the error of Balaam for reward. The word rendered ran greedily -- execuyhsan, from ekcew -- 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 Barnes "2 Pe 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 (apollumi) is often used to denote future punishment, Mt 10:28,39; 18:14; Mr 1:24; Lu 13:3,5; Joh 3:15,16

Joh 10:28; 2 Th 2:10; 2 Pe 3:9.

In the gainsaying of Core. Of Korah, Nu 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.

{a} "Cain" Ge 4:5 {b} "Balaam" Nu 22:7,21 {c} "Core" Nu 16:1