2 Peter 2:20

20.For if after. He again shews how pernicious was the sect which led men consecrated to God back again to their old filth and the corruptions of the world. And he exhibits the heinousness of the evil by a comparison; for it was no common sin to depart from the holy doctrine of God. It would have been better for them, he says, not to have known the way of righteousness; for though there is no excuse for ignorance, yet the servant who knowingly and wilfully despises the commands of his lord, deserves a twofold punishment. There was besides ingratitude, because they wilfully extinguished the light of God, rejected the favor conferred on them, and having shaken off the yoke, became perversely wanton against God; yea, as far as they could, they profaned and abrogated the inviolable covenant of God, which had been ratified by the blood of Christ. The more earnest then ought we to be, to advance humbly and carefully in the course of our calling. We must now consider each sentence.

By naming the pollutions of the world, he shews that we roll in filth and are wholly polluted, until we renounce the world. By the knowledge of Christ he no doubt understands the gospel. He testifies that the design of it is, to deliver us from the defilements of the world, and to lead us far away from them. For the same reason he afterwards calls it the way of righteousness. He then alone makes a right progress in the gospel who faithfully learns Christ; and he truly knows Christ, who has been taught by him to put off the old man and to put on the new man, as Paul reminds us in Ephesians 4:22 (174)