Ooh! If he refuses to back down on the Consequences thing, how about "Demonic infection" ?
Maybe he suddenly finds Hellfire backing up some of his attacks when he's really angry (Hellfire punch to the face type of thing). He knows that continuing to allow that to happen is likely to at best drive him away from God, and at worst Unmake the sword, but anger is so hard to control sometimes, the power is so useful, and "I'll give it up just as soon as I use it to take out X" is such an easy thing to think....