2 Peter 2:20-22
20 For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning.
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.
22 But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire.
The Grace New Testament Commentary - 2 Peter 2:20-22
2:20 When Christians therefore are duped into following the licentious lifestyle of such men, it is a serious matter if they do so after they have escaped the pollutions of the world through the knowledge of the Lord and Savior Jesus Christ. Peter is not referring here to newly saved individuals who are still struggling with sins they committed before they were saved. Instead, Peter is referring to people who have grown sufficiently in the knowledge of Jesus Christ so that their escape from the pollutions of the world has been real (cf. "actually" in v 18).
This word for knowledge in this epistle denotes the vehicle whereby God equips believers for holy living (2 Peter 1:3). To have found this knowledge powerful enough to liberate one from the pollutions of the world, and then to turn away from it back into depraved conduct, is serious indeed. It is so serious that for those who do this, the latter end is worse for them than the beginning.
This last idea, of course, does not suggest that such people (duped believers) end in hell (cf. John 6:35-40). On the contrary, it refers instead to the actual conduct of such people; since conduct is precisely what is being discussed. When anyone escapes an immoral lifestyle through the knowledge of the Lord, and then if he abandons the holiness he has found, he will sink more deeply than ever into the pollutions of the world.
The words "the latter end is worse for them than the beginning" very nearly reproduce the words of Jesus in Matt 12:45 and Luke 11:26, "the last state of that man is worse than the first." Although the Bible always affirms that salvation is absolutely free and can never be lost, it never treats a Christian's defection from God's path lightly. For a godly saved person to abandon the Lord's righteous standards is to court His righteous wrath and to invite tragic personal disaster. It is a fool's pathway (cf. v 22).
2:21 Therefore it would be better for Christians not to have known the way of righteousness than turn from the holy commandment delivered to them. Peter does not say that in such cases it would be better for a person not to have known Christ. Since eternal salvation is guaranteed by faith alone and cannot be lost, there are no circumstances under which not knowing Christ as Savior would actually be better. It is the path of righteousness that they would have been better off not knowing.
If a mature Christian, therefore, returns to corrupt behavior after walking in the path of righteousness, his time on that righteous pathway will prove counterproductive. Since a fall from that pathway leads to deeper degradation in sin, the time spent on the Christian road has led to a worse result than otherwise would have been the case.
A second thing Peter does not say is that such people turn from Christ. Rather they turn from the holy commandment delivered to them.
2:22 Those who follow this spiritual deception behave in a gross and degrading way. They behave like a "dog" that "returns" to eat its "vomit" or like a "sow" that has been all "washed" off but goes back to "wallowing" in its favorite mud hole. This pointed proverb is simply a straightforward and highly unflattering description of the conduct of those who heed the false teaching. They are behaving like disgusting animals!
Once again, of course, we observe here the uncompromising realism of the NT writers. They know the saving grace of God, but they refuse to gloss over the enormity of the failures to which believers are liable unless they stay close to the Lord and depend on His strength.
Charles Bing - Grace, Salvation, and Discipleship - A Dog Returns to His Vomit, 2 Peter 2:1-22
(Salvation) Interpretation: False teachers go to hell as well as those misled by them.
(Discipleship) Interpretation: False teachers go to hell, and those misled by them suffer a terrible fate.
It is clear that the false prophets and teachers mentioned at the beginning of this passage are unsaved and doomed to eternal destruction. The passage starts with a contrast between them and the "holy men of God" mentioned in the preceding passage (2 Peter 1:21). The language describing their eternal fate is explicit and unequivocal (2 Peter 2:3-17; cf. the parallel passage in Jude 1:4-6).
There seems to be a second group of people in this passage; it is those influenced by these false teachers to the point that they "follow their destructive ways" (2 Peter 2:2). These also appear to be unsaved. Since they are in contrast to the saved readers, a third group addressed directly ("you") in verse 3, they apparently profess to be Christians which causes the Christian way to be blasphemed when they are seduced.
This third group is the readers Peter is warning. They are referred to in a general way in verse 3 when Peter says that the false prophets "will exploit you with deceptive words." If Peter was writing to believers, as we will see he was, then he is warning about the effects that the false prophets have on those not saved (v. 2) and those to whom he writes who are saved (v. 3). After describing the doom of the false teachers and their unsaved followers, Peter directs his attention to this third group in verse 18. These believers are in danger of succumbing to the influence of the false prophets.
How do we know that the third group is comprised of saved people? They are called "ones who have actually escaped (or some translations: 'barely escaped' which also implies salvation) from those who live in error" (v. 18). They have "escaped the pollution of the world through the knowledge of The Lord and Savior Jesus Christ" (v. 20). The fact that they can be "again entangled" in the world's pollution means that they had once been, but had escaped (v. 20). Peter's statement in 2 Peter 2:21 makes it clear that they had "known the way of righteousness." Their fate, described by the contemporary proverbs cited in verse 22, require that the dog had once left its vomit, and the pig was once washed.
So, we see a shift in Peter's address. He writes to this group of believers to warn them of the unsaved false teachers among them who will be destroyed and have led others to the same fate (vv. 1-17). The change in address is clear. After indicting the false teachers in every verse from verse 10 through 17, the indictments stop abruptly. Then in verses 18 and 19, he discusses the danger of believers who might be seduced by the false teachers.
When Peter speaks of the fate of the believing readers who could be influenced by the false teachers, he speaks in terms of possibility, not certainty. These believers would face a terrible fate, but it is not specified as destruction or hell, only that their "latter end is worse for them than the beginning" (v. 20). Whatever struggles or trials they endured as new Christians will fade in comparison to the trouble that awaits them (perhaps temporally, or at the Judgment Seat of Christ, or both). Peter says it would have been better if they had not known "the way of righteousness" than to turn from "the holy commandment delivered to them" (v. 21). Peter is not saying that it would be better if they had never gotten saved. He is saying that it would be better if they had not known the teaching about the life of righteousness, implying that because they do, they have a greater responsibility to follow it. The text indicates this life of righteousness is defined by living according to "the holy commandment delivered to them." What is this holy commandment? Apparently, it is not related to any command to believe or be saved, as that would be an unusual and unprecedented way of referring to salvation. There are a number of options that this could speak of, for example, the command to love (John 13:34) or the command to be holy (1 Pet. 1:15). But both of these are commands to Christians, (Discipleship) commands.
It is naive to say that true Christians will not follow false doctrine. The apostle Paul was not convinced of such a notion - see Galatians and his many warnings to Christians about staying in the truth. Or, ask any pastor of tenure who has seen Christians come and go with the strangest of doctrines. It is especially sad to see and disconcerting to know that unless they repent of their error, there is a devastating fate that awaits them. It is best to avoid false teachers altogether and warn Christians about them.