 You may not have done it physically, but in your heart and in your mind you have done it. That's why he talks about lust. He's not upping the ante. Some people, and I've been guilty of this too, preaching that what Jesus does is he's actually upping the ante a little bit. No, he is causing you to really think about it. It's easy to say, well, I haven't committed adultery, but have I fantasized?