"Ye have heard that it was said by them of old time, Thou shalt not commit adultery: But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart. And if thy right eye offend thee, pluck it out, and cast it from thee: for it is profitable for thee that one of thy members should perish, and not that thy whole body should be cast into hell. And if thy right hand offend thee, cut it off, and cast it from thee: for it is profitable for thee that one of thy members should perish, and not that thy whole body should be cast into hell" (Matthew 5:27-30)
This passage teaches us at least three things about all sin. First, sin begins in the heart. Jesus taught that evil proceeds from the hearts of men (Mark 7:21-23). In order to rid his life of sin, a person must control the thoughts of his heart (Philippians 4:8).
Second, the pleasures of sin are only temporary. One brief moment of sin can cause a person to experience the consequences of sin for a lifetime, perhaps an eternity. In light of the fleeting nature of the pleasures of sin, why would anyone be willing to "take a chance" on the fate of their soul? Jesus taught that we are to remove any obstacles in our lives that come between us and heaven.
Third, the punishment for sin is real. Hell is a place where there will be weeping and gnashing of teeth (Matthew 25:30). Hell is pictured as a lake of fire, where Satan himself will one day be cast (revelation 20:10). Hell is a place of conscious, eternal punishment (Matthew 25:46).