Phanuel/Uriel (literally, "the Fire God") is not only the angel that is set over repentance/penance, he is also the angel that is set over Tartaros, aka the fiery place of torture where the souls of the unrepentant wicked end up after death.

Some say he is one of the four aspects ("faces") of God, together with the better known Michael, Gabriel and Rafael.

Now you have to realize that to undergo penance for your sins is not a very pleasant thing. You are basically voluntarily undergoing torture during your lifetime, to escape an even greater torture after death. And "the Fire God" is set over both the torture of penance during your lifetime, as well as over the torture in Tartaros.

He wasnt very popular with the corrupt and unrepentant clergy of the Middle Ages, for obvious reasons. They actively cracked down on anything related to Phanuel/Uriel. Then again, worshipping someone who oversees your "chastening", might be a little masochistic.

The word Uriel (Fire-God) implies that he could somehow be related to another well known angelig being, known to muslims as Iblis, who according to the Quran was created from fire and refused to serve the humans out of pride.

He might be related to the christian "Satan", the accusator, the fiery "Dragon".