The Change Within
A new-born Christian is not reformed by individual efforts. Even if he or she could change themselves, they would mess it up because they would take the credit. The change believers so desparately need and want in their lives comes in the person of Christ residing within them.
Ephesians 3:17 That Christ may dwell in your hearts by faith . . .
1 John 4:4 Greater is He that is in you, than he that is in the world.
Christ within gives us a desire for holiness, for God, and for heaven. It's not that we can't sin again -- we can. But we don't want to.