Jesus tells us in Luke 12:5 the God has to power to cast folks into hell, and implies that he will do exactly that when some folks are judged. The question is, however, does Jesus mean what so many modern Christians understand him to mean? The Greek word Jesus used for hell is gehenna (G1067). The word is derived from Hinnom, the name of a valley just off the southwest wall of Jerusalem. It was a place where some of the kings of Judah sacrificed their children to the Phoenician god, Molech. King Josiah destroyed its altars and filled it with dead bodies in order to make it unclean for any kind of worship. Later the Jews turned it into a garbage dump where they burned the city’s refuse.
The idea Jesus expresses in Luke 12:5 is not that wicked people are garbage, but that their sins are garbage, and fire is a purifying element, in that it separates what is good (Genesis 1:31) from the dross (Proverbs 25:4; 26:23; Isaiah 1:25). Even if all the works of the wicked are nothing but wood, hay and stubble—fuel for the fire—still it doesn’t mean the wicked will suffer for eternity (1Corinthians 3:11-15). Such thinking goes beyond the intent of God’s word (2John 1:9). Rather, it is only until the dross is burnt away, if the analogy in the Scripture can be trusted. The writer of Hebrews offers an analogy of seeds planted in the earth; one seed brings forth herbs, while other bring forth briars and is near to being cursed, “whose end is to be burned” (Hebrews 6:7-8). Notice that the earth is not destroyed when it is burned; only the fruits of the earth are destroyed. That is, one’s works / sins are destroyed. Elsewhere Jesus tells us that the earth is like a man’s heart into which the seed or word of God is sown (cf. Luke 8:11-12).
So, how then have we come to believe that the wicked are punished eternally? Eternal punishment is a concept developed in the Church by people with questionable motives. Most notable is Augustine’s teaching on this subject. Augustine had come out of Manichaeism, a Gnostic religion wherein fire was a great part of his understanding of punishment. Without making a judgment about Augustine’s authenticity as a believer, I do believe his understanding of God’s love for the sinner is deplorable, yet he is largely responsible for our modern Christian understanding of an eternal hell. I believe Augustine had a tortured conscience over the sins he had committed, and once he left Manichaeism and became a Christian, he brought with him much of the Gnostic error it preached on this subject and sought to blend it, whether ignorantly or purposefully (God knows), with Biblical ideas. Gnosticism is difficult to understand, and the quote below uses terms not familiar to our modern Christian understanding, so some portions of the excerpt have been deleted. If, however, one wishes to read the whole thing, simply click on the link provided at the end of the excerpt. Notice that according to:
“Manichean eschatology …A universal conflagration ensues and burns on till nothing but lightless cinders remain. This fire continues during 1486 years, during which the torments of the wicked are the delights of the just. When the separation of light from darkness is finally completed, all angels of light who had functions in the creation return on high; the dark world-soul sinks away in the depth, which is then closed forever and eternal tranquility reigns in the realm of light, no more to be invaded by darkness. …Sinners, however, must, after death wander about in torment and anguish, surrounded by demons, and condemned by the angels, till the end of the world, when they are, body and soul, thrown into hell.” [Catholic Encyclopedia: Manichaeism] (emphasis mine)
There isn’t a great deal of difference between this Gnostic belief and what modern Christianity understands as eternal punishment. Nevertheless there is no such thing as eternal punishment. The Bible doesn’t teach it. In order for a Christian to support the doctrine of eternal punishment, he must go outside of the Bible in order to do so. What the Bible does teach is an age-lasting corrective discipline that will bring unrepentant sinners to embrace the will of God. The Scriptures tell us that God wants to save all men (2Timothy 2:4), and he works all things out according to his own will (Ephesians 1:11). If this is so, how would it be possible for anyone to miss the salvation of God, who has already saved all men (1Timothy 4:10), so, if all men haven’t come to repentance, it must follow there will come a season in the judgment when all men will repent. Repentance is a gift given to us by God (2Timothy 2:25). It is not something we are able to do by ourselves.
 Remember, Jesus warned his disciples of the leaven of the Pharisees, which is hypocrisy (Luke 12:1), but earlier leaven was used to denote their doctrine (Matthew 16:6, 12). Spiritual warfare was not a danger exclusive to the first century. The Pharisees and Sadducees were examples of those who would come later and would seek to control the affect of Gospel of Christ by adding their thought to it or taking power from it, thereby diminishing Jesus’ rule in our lives as our Christ and the Savior of the world.
 I have nine studies on the subject of eternal punishment (to which I have added this present study), which I list on my page: Is There a Hell? They are there for anyone who cares to study this matter for himself. I list plenty of Scriptures that should help anyone who undertakes such a study to understand whether or not I am forcing the Scriptures to support my doctrine. Anyone, who comes to the study without a prior bias against what I have to say, should be able to see for himself or herself what the truth really is.