2 Peter 2:22 KJV
[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.”
When we consider these two animals, we must first note that neither one is behaving abnormally. A dog returning to vomit and a pig returning to mud are acting in accordance with their nature. Peter is describing people who have experienced some level of cleansing or escape from corruption, yet went back to it. Salvation is not about self-improvement, but a transformation that takes place in the heart. You can clean up the outside, but if the heart has not changed, then it is only a matter of time until the individual returns to what he was before.
The dog teaches us that it is foul within, and the sow teaches us that it is filthy without. The dog has a foul appetite, while the sow has a filthy appearance. These are very vivid illustrations of apostates. They are corrupt on the inside and the outside. You can see it in their desires and actions.
However, it is also true regarding one who is living a self-reformed life. Self-reformation only brings more corruption. It develops pride and abandonment from God. It teaches one to trust himself and think too highly of himself. He feels that he has accomplished something on his own to better himself. The truth is that you cannot expect an unclean person to live a clean life.
Years ago, I remember a preacher using this illustration. Before he was saved, he was known to use profanity. After he was converted, he went to work and notified his co-workers that He had been born again and no longer used that kind of language. One of them declared that he could also stop swearing, just like any religious man could. The preacher made it clear that he had changed his ways because he wanted to please his Savior. Every day, the man would remind the preacher that he was no longer swearing, and he didn’t have to be religious. The sinner was proud of how he had accomplished this and continued to make it a subject of daily conversation. Then, one day, he was hammering a nail and hit his thumb with full force. At that moment, the man launched into a profanity-laced outburst. This is not to say that a believer could not swear. The point of the illustration is that the man returned to his old ways because that is what was in his heart. Salvation changes a man from the inside and gives him a new nature. He has new desires and no longer wants to live a filthy lifestyle.