Today I am going to put Mark 9:42-48 into my own words:
Be careful about leading those who believe in me to sin. You'd be better off being drowned in the sea than doing that. And also be careful about letting sin take over your life. Get rid of anything in your life that causes you to sin, even if it is painful to do that. It's better to enter the kingdom of God missing some of the things that are important to you than to miss out on that kingdom and end up in hell, which is a terrible place of eternal torment.
When Jesus talks about cutting off hands and feet and plucking out eyes, He is obviously using hyperbolic language to emphasize the drastic effects of sin. Ultimately, unless our sins are dealt with through faith in Jesus, we will end up in a horrible place of eternal torment. The hell Jesus is speaking of here is not merely symbolic or allegorical - it is a physical place that will be a horrible, permanent existence for anyone who ends up their. The good news is that by putting our faith in Jesus, no one ever has to experience it.
But even for those who have put their faith in Jesus, this is a warning that we need to sometimes take drastic measures to make sure sin does not get a foothold in our lives.