Then was Nebuchadnezzar full of fury, and the form of his visage was changed against Shadrach, Meshach, and Abednego: therefore he spake, and commanded that they should heat the furnace one seven times more than it was wont to be heated.
The form of his visage was changed. He had shown forbearance (Daniel 3:14-15) as a favour to them; but, now that they despise even his forbearance, anger 'fills' him, and is betrayed in his whole countenance.
Therefore he ... commanded that they should heat the furnace one seven times more than it was wont - literally, 'than it was (ever) seen to be heated.' Seven is the perfect number - i:e., it was made as hot as possible. Passion overdoes and defeats its own end, because the hotter the fire the sooner were they likely to be put out of pain.