You have heard that it was said, ‘You shall not commit adultery.’ But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart. If your right eye causes you to sin, tear it out and throw it away. For it is better that you lose one of your members than that your whole body be thrown into hell. And if your right hand causes you to sin, cut it off and throw it away. For it is better that you lose one of your members than that your whole body go into hell.
"It was also said, ‘Whoever divorces his wife, let him give her a certificate of divorce.’ But I say to you that everyone who divorces his wife, except on the ground of sexual immorality, makes her commit adultery, and whoever marries a divorced woman commits adultery.
God is not just concerned with our actions, he is concerned with our thoughts. God does not just desire mere outward obedience to his ways, he desires that we think how he thinks. We do not think that Jesus means that we are to literally pluck out our eyes or cut off our hands. He wants us to see the seriousness of our thoughts and to strengthen our resolve to resist wicked thoughts.
Sexual sins are some of the most powerful ones we will experience in life. Jesus used a strong example to make a strong point.
Jesus established a high standard for Christians to live by. Marriage is not something to be taken lightly.