“If people escape the moral filth of this world through the knowledge of our Lord and savior Jesus Christ, then get tangled up in it again and are overcome by it, they are worse off than they were before. It would be better for them never to have known the way of righteousness than, having come to know it, to turn back from the holy commandment entrusted to them. They demonstrate the truth of the proverb: “A dog returns to its own vomit, and a washed sow wallows in the mud.” II Peter 2:20-22 GNT
It would appear that the ‘sow, having washed and return to wallow in the mud’ reinforces the same sentiment that it does not make sense to be washed, to be cleansed, to be purified and to become filthy with sin once again.
The person who makes an outward profession, absent of an inward transformation will soon return to the old way of life.
Likewise, the apostate gives an initial display of repentance and outward change as though they had embraced the truth. It becomes evident eventually that their nature has not changed.
This coupled with their rejection of the truth, indicates that they were never spiritually transformed. (Titus 3:5) They are still worldly in nature.
The apostates with their religious profession along with some outward change soon revert to the dictates of their real nature. Individually, each one of them is still the corrupt “old man,” controlled by his lust. (Eph. 4:22)
Peter had explained the dynamics of the new nature earlier in II Peter 1:3-4. The new nature produces godly living, which brings glory to God. The new nature prevents believers from ever returning to the filth and immorality of this world. We have escaped the pigpen of the world and God intends that we remain free from it.
A dog may return to its vomit, a pig may return to the mud, but a true Christian will return as the Prodigal Son to the Father.
“My friends, watch out! Don't let evil thoughts or doubts make any of you turn from the living God. You must encourage one another each day. And you must keep on while there is still a time that can be called "today." If you don't, then sin may fool some of you and make you stubborn”. Heb. 3:12-13 CEV