Daniel’s three companions are tested in their faith to God. They refuse to bow down to a false image that the king has set up. He becomes furious and has a fiery furnace heated up seven times hotter then normal and has the three companions of David thrown in! The strong men who throw them in die from the heat but the companions of David are seen walking in the midst of the furnace and are summoned out by the frightened king. The fire had no effect on them. They did not even have the smell of smoke on them! The king is elated and allows freedom of worship for the Hebrews!
The main point is that the three knew that they might die but they loved Almighty God more than themselves and were rewarded! Compare where Jesus mentioned that one should love God with your whole soul in Matthew 22:37-39!