"I think if Eternity held torment, its form would not be fier..." — Charlotte Brontë quote meaning

I think if Eternity held torment, its form would not be fiery rack, nor its nature, despair. I think that on a certain day amongst those days which never dawned, and will not set, an angel entered Hades — stood, shone, smiled, delivered a prophecy of conditional pardon, kindled a doubtful hope of bliss to come, not now, but at a day and hour unlooked for, revealed in his own glory and grandeur the height and compass of his promise: spoke thus — then towering, became a star, and vanished into his own Heaven. His legacy was suspense — a worse boon than despair.