The devouring fire is not a punishment from outside. It is the power at the deep center of a person, the force people have always called God, and it burns because it is real and cannot be bargained with. Those who tremble lived on the surface and pushed their darker parts out of sight. When that buried self rises, meeting it feels like being consumed.
But the fire destroys only what is false. The one who can stand in it has already faced his own hidden self, so nothing in him is left pretending and the fire finds nothing to burn. That is why he can live beside a flame that still terrifies everyone hiding from themselves.