I'm not sure exactly what you mean, but as the helpfiles suggest, being proficient at these skills makes you better at using scrolls. Basically, you fail ("mispronounce a sylable") less often.

Scrolls (recite) seems to have a base chance that varies by class. Mages being better than bards and thieves and whatnot. When you recite, your chances of being successful are improved by being proficient in the skills the helpfile references. In the case of arcane lore, it sounds like your "base chance" is that of a mage instead of a regular dumb 'ol thief.

Other things, like intelligence, also play a part as I understand it.

None of that is first hand experience, FWIW, but I'm pretty sure it's accurate.