Also, limiting Harry's access to knowledge (warning off the other profs, warding the books, etc) makes Quirrell the sole conduit for advanced knowledge for Harry. (Or at least limits the competition). And Quirrell implied to Harry that he was at his nearly-unrestricted service. That gives Quirrell more access to Harry's thought processes (by the questions he asks) and more capacity to steer his choices.
As to what he's steering them toward, he pushed Harry off of new spells, which makes me wonder if he has an old one in mind. There was talk about rituals of sacrifice here (the blood-to-fire) and generally recently (Tracy Davis's invocation). It's possible that there's some ritual that Quirrell would like Harry to perform, not for what it manifests, but for the changes it makes to the caster.
He probably also wants to push Harry away from new spells for safety reasons (presumably he thinks Harry might try to science up a dangerous new spell and that's how he ends the world; he has some experience with Harry attempting to combine magic and science from Azkaban). If he personally steers Harry towards old spells then at least he knows what those spells do.
It's also possible that the Restricted Section contains enough information for someone like Harry to figure out how to create spells from reading it.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 90. The previous thread has passed 750 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18,19.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: