In Mark 9:43-48, Jesus is reported to have said:
If your hand causes you to stumble, cut it off; it is better for you to enter life crippled, than, having your two hands, to go into hell, into the unquenchable fire, [where their worm does not die, and the fire is not quenched.] If your foot causes you to stumble, cut it off; it is better for you to enter life lame, than, having your two feet, to be cast into hell, [where their worm does not die, and the fire is not quenched.] If your eye causes you to stumble, throw it out; it is better for you to enter the kingdom of God with one eye, than, having two eyes, to be cast into hell, where their worm does not die, and the fire is not quenched.
The idea of eternal punishment offends a lot of people today, even among believers. And not just today, either—a number of the ancient Church Fathers tried to soften this doctrine by turning it into a kind of pre-Catholic purgatory, where sinners go to get the sin burned out of them so that they then can enter into the eternal blessings of heaven. But Jesus wasn’t one to try and accommodate what you might call the harsh teachings of Christianity with the nice-guy sensibilities of the meek and moral. All of his reported teachings on hell, like the passage above, assume that once you’re thrown into hell, you stay there.