“Now may the God of peace Himself sanctify you completely; and may your whole spirit, soul, and body be preserved blameless at the coming of our Lord Jesus Christ. He who calls you is faithful, who also will do it” (1 Thess 5:23-24).
There it is, what we might call the punchline promise. When all is said and done, God will have pulled it off, sanctifying you so completely that not an iota of the old life remains. He will do it!