It is the only one of Jesus' parables which explains the work of the kingdom after it has been set up. The sheep in the parable represent the people who willingly learn of the love and righteousness of the Heavenly Father and his Son, Jesus Christ, and strive to obey the laws of the kingdom.
Many scriptures use fire as a symbol of destruction.
God never intended for mankind to think of fire as his punishment for sin. He is a God of love and mercy and would never torture any creature forever in such a terrible way. Because fire destroys things so completely, the Bible often uses it to show total destruction. The garbage dump of Jerusalem was in the Valley of Hinnom, where a fire was kept burning constantly. Not only was garbage thrown into it, but also dead animals and even the bodies of vicious criminals whom no one had bothered to bury.