Matthew 5:27-28 KJV
27 Ye have heard that it was said by them of old time, Thou shalt not commit adultery: 28 But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.
Once again, Jesus is talking about the heart. What we do and what we say all start in the heart. If we allow lust in our hearts, it won't be long before action is taken. We must stop it before it starts.
Why let sin take hold of our hearts? We are held to a higher standard for a reason-because God expects more from us. He gives us guidelines and rules to protect us from the mistakes of this world.