Those who are truly born of God have received a new nature, a divine nature and are new creations in Christ. They have been transformed from pigs and dogs into sheep. The change is more than merely outward/cosmetic, as in 2 Peter 2:20. *These cleaned up on the outside dogs and pigs were never sheep.
Compare 2 Peter 1:4 - "partakers of the divine nature, having escaped the corruption - Strongs #5356 that is in the world through lust with 2 Peter 2:20 - with they escaped the pollutions - Strongs #3356 (different Greek word) of the world through the knowledge of the Lord and Saviour Jesus Christ, yet they are again entangled therein, and overcome. *Notice that 2 Peter 2:20 did not mention them being "partakers of the divine nature."
Corruption (Strongs #5356) which describes corruption, destruction, decay, rottenness, decomposition. Internal corruption.
Pollutions/Defilements (Strongs #3393) describes pollution, defilement; a stain. Pollutions/Defilement refers to what is on the outside (2 Peter 2:20). But genuine believers have escaped the corruption that is in the world through lust (2 Peter 1:4).
Corruption is deeper than pollutions/defilements on the outside: it is decay on the inside.
Having the knowledge of Jesus Christ does not save a person if there is no heart submission to that knowledge. The latter end is worse than the beginning for these people because rejecting this knowledge will make them more accountable at the judgment. Judas Iscariot is a good example of someone who rejected the knowledge of the Lord and Savior Jesus Christ, yet was never saved.