There is a quest in the House Telvanni questline that requires you to know certain spells, however custom versions of those spells don't count, because the vanilla Morrowind scripting engine can't detect them, but with the new MWSE functions by Merzasphor it is possible now, and this mod does it for that quest. The exact quest is listed at the bottom of the readme.

Requires Merzasphor's MWSE Update, which is newer than the one included in MGE XE. If using MGE XE, disable its version of MWSE in its settings.