2 Peter 2:20

For if after they have escaped the pollutions of the world The word "escaped" had been used above (2 Peter 2:18) of the followers. Here, as the context shews, in the repetition of the word "overcome" from the preceding verse, it is used of the teachers themselves. They also had once fled from the pollutions of heathen life and heathen worship into which they had now fallen back.

through the knowledge of the Lord and Saviour Jesus Christ The word for "knowledge" in the Greek is the compound form (ἐπίγνωσις) which is always used by St Paul (e.g. Ephesians 4:13; Colossians 2:2; Colossians 3:10; 1 Timothy 2:4), and had been used by St Peter (chap. 2 Peter 1:2-3; 2 Peter 1:8), of the highest form of knowledge which is spiritual as well as speculative. The false teachers had not been all along hypocrites and pretenders. They had once in the fullest sense of the words "known Christ" as their Lord and Saviour. There is, perhaps, no single passage in the whole extent of New Testament teaching more crucial than this in its bearing on the Calvinistic dogma of the indefectibility of grace. The fullest clearness of spiritual vision had not protected these heresiarchs from the temptations of their sensuous nature.

they are again entangled therein, and overcome The verb "entangled" is used also by St Paul (2 Timothy 2:4). It describes vividly the manner of the fall of those of whom the Apostle speaks. They had not at first contemplated the ultimate results of their teaching. It was their boast of freedom which led them within the tangled snares of the corruption in which they were now inextricably involved.

the latter end is worse with them than the beginning Literally, the last state has become worse than the first. The last words are so distinctly a citation from our Lord's teaching in Matthew 12:45, that we are compelled to think of St Peter as finding in the history of the false teachers that which answered to the parable of the unclean spirit who was cast out of his house and returned to it with seven other spirits more wicked than himself.