2 Peter 2:18

For when they speak great swelling words of vanity Literally, For speaking.… The adjective is used by classical writers both literally and figuratively of excessive magnitude. It indicates what we should call the "high-flown" character of the language of the false teachers. "Vanity" is used in its proper sense of "emptiness." There was no substance below their show of a transcendental knowledge. Here again we trace a parallel with St Paul's language, "Knowledge puffeth up" (1 Corinthians 8:1).

they allure through the lusts of the flesh, through much wantonness Better, they entice in the lusts of flesh (describing the state of the tempters) by acts of lasciviousness (as the dative of the instrument). The word for "allure" is the same as in 2 Peter 2:14. In "wantonness" we have the same word as in 2 Peter 2:2; 2 Peter 2:7.

those that were clean escaped from them who live in error Some of the better MSS. give those who were a little (or partially) escaping … In the one case, stress is laid on the fact that the work of a real and true conversion was marred by the impurity into which the victims were afterwards betrayed; in the other, on the fact that their conversion had been but incomplete, and that therefore they yielded readily to the temptation. A possible construction of the sentence would be to take the last clause in the Greek in apposition with the first, "those that had partially escaped, those that live in error," but the English version gives a preferable meaning. In the verb for "live" we have a cognate form of St Peter's favourite word for "conversation" or "conduct" (1 Peter 1:15; 1Pe 1:18; 1 Peter 2:12; 1 Peter 3:1-2; 1 Peter 3:16).