"You have heard that it was said, 'Do not commit adultery.' But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. If your right eye causes you to sin, gouge it out and throw it away. It is better for you to lose one part of your body than for your whole body to be thrown into hell. And if your right hand causes you to sin, cut it off and throw it away. It is better for you to lose one part of your body than for your whole body to go into hell." Matthew 5:27-30
In the Old Testament, the commandment to abstain from adultery was seen more as matter of stealing another man's wife than it was a matter of purity. Here, Jesus makes it clear that adultery deals with the purity of the body, and He takes it a step further to make sure the people know that it is also a matter of the purity of the heart. Jesus (and therefore, also, God) has always been and will always be mainly concerned with the condition of our hearts. He knows that we will mess up in life, but longs for our hearts to be drawn to and connected with His.
Gouging out your eye and cutting off your hand are not literally recommended. Jesus is saying that sin is a serious issue, and, as such, should be dealt with in a radical and serious manner. Don't just try to change things, be radical about what you need to do to remove the temptation to sin and to abstain from sinning, not so you can be pious, but so you can be closer to the heart of God.
May you be serious about your sin today. Pray that God will reveal sin to you that you were not aware of, or that you were hiding from others. Confess these sins to God, and to other Christ-followers. Then, be radical about the ways you intend to deal with your sin, so that you may walk closer with God.