For those who are serious, Jesus shows us that sinners would be cast into Gehenna.
43 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:1
44 Where their worm dieth not, and the fire is not quenched.
45 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:1
46 Where their worm dieth not, and the fire is not quenched.
(Mk. 9:43-46 KJV)
The word translated hell is Gehenna. In this passage Jesus alludes to a prophecy from Isaiah. He spoke of being cast into the fire that shall never be quenched. A place where the worm does not die. This is from Isaiah 66.
22 For as the new heavens and the new earth, which I will make, shall remain before me, saith the LORD, so shall your seed and your name remain.
23 And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me, saith the LORD.1
24 And they shall go forth, and look upon the carcases of the men that have transgressed against me: for their worm shall not die, neither shall their fire be quenched; and they shall be an abhorring unto all flesh.(Isa. 66:22-1:1 KJV)
We know this place Isaiah writes of is Gehenna because Jesus called it Gehenna. Notice here however that is dead bodies that are burning, not souls or spirits. So, when Jesus spoke of being cast into Gehenna, it's dead bodies that will burn, not living souls or spirits. We also know that this place will not burn forever because Jeremiah also prophesied of this place.
38 Behold, the days come, saith the LORD, that the city shall be built to the LORD from the tower of Hananeel unto the gate of the corner.
39 And the measuring line shall yet go forth over against it upon the hill Gareb, and shall compass about tAso Goath.
40 And the whole valley of the dead bodies, and of the ashes, and all the fields unto the brook of Kidron, unto the corner of the horse gate toward the east, shall be holy unto the LORD; it shall not be plucked up, nor thrown down any more for ever. (Jer. 31:38-40 KJV)
As we see here the whole valley of dead bodies and ashes will one day be made holy to the Lord. Again, it's dead bodies, not living souls or spirits. It's not going to burn forever, if it's going to one day be made holy to God. Jesus tells us that sinners will be cast into Gehenna. In Revelation John said sinner would be cast into the Lake of Fire. The only way to reconcile these is to understand that Gehenna and the Lake of Fire are the same place. Revelation is a book full of symbolism. Gehenna is a valley, if it was full of dead bodies that were burning it would appear to be a lake of fire. I think the symbolism is pretty clear.