The fact of the reality of Hell is taught throughout the Bible in innumerable passages. The Lord Jesus Christ Himself probably had more to say about it than anyone else. He was a teacher with the most impressive credentials--a sinless life, a miraculous ministry, and an empty tomb that could not hold Him.
Christ is often spoken of as "Gentle Jesus, meek and mild," but that label hardly fits with the language we find in Mark chapter nine as He affirms the fact and reality of Hell. We read these strong statements:
"And if thy hand offend thee, cut it off: it is better for thee to enter into life maimed, than having two hands to go into hell, into the fire that never shall be quenched: Where their worm dieth not, and the fire is not quenched. And if thy foot offend thee, cut it off: it is better for thee to enter halt into life, than having two feet to be cast into hell, into the fire that never shall be quenched: Where their worm dieth not, and the fire is not quenched. And if thine eye offend thee, pluck it out: it is better for thee to enter into the kingdom of God with one eye, than having two eyes to be cast into hell fire: Where their worm dieth not, and the fire is not quenched."
-Mark 9:43-48
In another passage Christ calls the Scribes and Pharisees a "generation of vipers," and warns them, "How will you escape the damnation of Hell?" (Matt. 23:33) Those are pretty strong words from the Lord Jesus. He laid it on the line. He told it like it is.
When smaller questions the fact and reality of Hell, he's actually questioning the authority of the Bible, and the authority of the Lord Jesus Christ Himself. The Christian faith is all tied up together, and when it is attacked at one point, it becomes vulnerable at all. It holds together beautifully.