It had been better for them not to have known; their sin had been less if they had not known the truth, but now they sin against knowledge, and therein their apostacy is much worse than their ignorance would have been. The way of righteousness; the way of obtaining righteousness by Christ, and of living godly in Christ, 2 Timothy 3:12, prescribed in the gospel; the same which is called the right way, 2 Peter 2:15, and the way of truth, 2 Peter 2:2. The holy commandment; the same in other words. It is called holy, not only as proceeding from God, who is holy, but as teaching nothing but what is holy, and being the means God useth in making men holy, and as being opposed to the pollutions of the world before mentioned.
Related Commentaries of 2 Peter 2:21
2 Peter 2:21
21 For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them.