The seventh command tells us we are not commit adultery. Many people might say, "Well, I've never done that." But then Jesus said again in the Sermon on the Mount, "You have heard that it was said to those of old, 'You shall not commit adultery.' But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart." (Matthew 5:27–28). Of course, this applies to women as well: adultery also can be looking at a man lustfully.
This word Jesus used for "look" does not just mean a casual glance, but in the original language, refers to the continuous act of looking. In this usage, the idea is not that of an incidental or involuntary glance, but one of intentional and repeated gazing.
Jesus is not speaking here of unexpected and unavoidable exposure to sexual temptation. He is speaking of one who intentionally puts himself or herself into a vulnerable place. You understand the difference. We all live in a very wicked world, and tragically today, we don't need to go very far to see things that would be sexually explicit. Television is one place to start. Then of course, there is the Internet. Even if have been careful to avoid these things in your home, when you walk into a mall or a store today, there will be monitors playing videos, plus billboards and advertisements all around you. So we are constantly being exposed to these things.
The person Jesus is describing who commits adultery in his or her heart is one who would intentionally put himself or herself into a place of obvious temptation. Those who love God and want to please Him won't want to do this.