It is really a hard quest. Are you level 60? Then you can improve your glyphes to get more life. Also you can craft epic equip and take offhand to increase your holy resistence. The green carnifex scroll is very helpful, too. Use your best runes for def. I can't think of anything else, which could help you...
Btw you can't use seal, fervor or balms of resistence. They will be removed, when you are starting the flight :/
Hah! I did it on a summie with just a few pieces of level 57 epic crafted armour, the remains of my set of 51/52 leggie gear, crappy blue and green 51 non-upgradable glyphs, level 444/444 runes, and a staff. No carnifex scrolls, several WM rubies missing.
OP: When the context skill comes active, spam it like nothing else exists and like your character's life depends on it (it does!). Do not stop until you reach the end of the flight. In particular, the quest calls on you to kill a certain number of the demons, but the demons keep coming after you have killed that many, and you will be killed just as dead if you relax after killing the required number as if you didn't spam hard enough at the beginning.
So to repeat, because it is critically important: as soon as the skill comes active, spam it like a madman, and don't stop until the fish drops you on the platform at the top of the tower. There's more fighting after that, but nothing really serious compared to the demons.