You will know them by their fruit. (Matt. 7:20) Obedience, obedience, obedience is the fruit of a Christian. It is only through the power of the indwelling Holy Spirit that one overcomes sin.
"And being made perfect, he became the author of eternal salvation unto all them that obey him;" Heb. 5:9
"Then said Jesus to those Jews which believed on him, IF ye continue in my word, then are ye my disciples indeed;
And ye shall know the truth, and the truth shall make you free." John 8:31-32
Matt 7:20-21
Wherefore by their fruits ye shall know them.
Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
KJV