"Last week in a Bible study our pastor read Revelation 6.8. In that verse he read that Death and Hades were sent to earth. In my Bible the translator used hell. When I asked our pastor he said there was a difference between Hades and hell. What's the difference?"
Your pastor is correct in his assessment, for indeed Hades and hell are two different concepts-at least, they used to be. Originally, Hades was a Greek god of the underworld. In the ancient Greek mind, the underworld was not a place of torment nor punishment. It was simply a place where mortals went after death. In their mythology the dead were escorted to the river Styx and for a price they were sailed across to their eternal home. Their concept of heaven was such that only the gods could reside there (with a few apparent exceptions in the literature).
When the Old Testament was translated into Greek the term Hades was used to translate the Hebrew Sheol. Throughout most of the Old Testament times there was no notion of an afterlife; death was the end of existence (cf.., Psalm 6.5, 49.14, Job 7.9) and euphemistically one went down to Sheol, or to the place of the dead. Thus Hades came to indicate not so much a Greek god, but a place-even in the Israelite mind. So, by the time of Jesus there was a split between the orthodox Jews (Sadducees) who believed scripture taught there was no afterlife and the liberal Jews (Pharisees) who believed in both heaven and hell.
But even with the Pharisees Hades did not equal hell. They had their own word for the place of eternal damnation and punishment. And that word was Gehenna. Originally, Gehenna was the garbage dump on the southwest side of Jerusalem. It was also the site of earlier child sacrifice (cf., 2 Chronicles 28.3, 33.6, Jeremiah 7.31, 32.35). To dispose of the garbage appropriately, the dump was continuously set afire. Thus, the dump came to symbolize a place of eternal punishment "where their worm never dies, and the fire is never quenched" (Mark 9.48). Gehenna is the word from which we get the word hell in our Bible. It is the word Jesus used most often to describe the place of punishment.
In the book of Revelation the term Gehenna is never used. Instead, Hades is used. However, the question then becomes, is Hades being used by the author to indicate a place of eternal torment, i.e., as a synonym for Gehenna, is it being used in the sense of the place of the dead, i.e., as a synonym for Sheol, or does it designate the Greek god?
The word is found in four places in the Revelation: 1.18, 6.8, 20.13, 20.14. In all four places Hades appears with Death. Both terms seem to indicate a personification of the two concepts, thus it is quite possible Hades does not represent either a place of the dead or a place of torment. In fact, in Rev. 20.13-14 it is clear that both Death and Hades are personifications: "And the sea gave up the dead that were in it, Death and Hades gave up their dead, and all were judged according to what they had done. Then Death and Hades were thrown into the lake of fire. This is the second death, the lake of fire" (Revelation 20:13-14). Thus we see that the author certainly did not see Hades as the place of torment, but as a personage.
In the New Testament the word Hades seems often to be used as synonymous with Hell, a place of eternal torment. However, clearly this is not always the case and the reader should be aware of the subtle differences. When studying the Revelation, or any scriptural passage, make sure you use multiple versions so you may catch these translation differences, like when hell is used instead of Hades.