Bible Verses About internal sin

But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.

But those things which proceed out of the mouth come forth from the heart; and they defile the man.

And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.