The doctrine that says that if you still commit sin that you are still sinless by faith in Jesus, and that it is the physical body which is the root of all sin (because by nature it is not perfect and subject to death) is a Gnostic heresy.

(1 John 3:5-9 KJV) "And ye know that he was manifested to take away our sins; and in him is no sin. Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither known him. Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous. He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil. Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God."

(John 8:36 KJV) "If the Son therefore shall make you free, ye shall be free indeed."