In High Gate ruins, you meet a woman called Anska. Anska believes that there is a scroll within the tomb which contains records that link her family to Ysgramor's lineage. She asks for your help in procuring the scroll because it's guarded by a dragon priest, Vokun. At the end of the dungeon, you destroy Vokun and find the scroll in question, at which point you have the option to give it to Anska or refuse to give it to Anska. If you give it to her, she rewards you and mentions that the scroll is encrypted, so it may take some time to decipher. If you refuse to give her the scroll, she turns hostile, and you get to keep the scroll... Which cannot be used in any way and is valueless. My mod adds a use for the scroll, thus making keeping the scroll a viable choice for a reward rather than just a needlessly mean thing to do.

If you keep the scroll then try to read it, you will find that it is, indeed, encrypted. You cannot read it here and now; you will need access to the correct resources to decrypt it... Perhaps a library has the records you seek. If you then take it to the Arcanaeum in the College of Winterhold then try to read it there, a couple hours will pass, and you will successfully decipher its content. It turns out Anska had bad information; the scroll bears no references to Ysgramor, let alone any families linked to his lineage. Instead, it contains knowledge coveted by the Dragon Priest, Vokun. The contained insights will give you a small permanent buff to magic resistance and magicka regeneration (10% and 15% respectively), as you come to a greater understanding of the nature of magic. After you have finished decrypting the scroll, you can then sell it for a higher value (500 gold base value). Presumably you are selling it with your translations and notes, thus making this knowledge valuable.

FAQ

-How do I read the scroll?
It's a misc item in your inventory, but you can still use it by clicking on/activating it in your inventory. Just be sure to stop by the Arcanaeum in order to successfully read it.

-Why is the buff you get so magic-focused?
Vokun's mask bears an enchantment that fortifies magic skills. He was presumably a talented mage in his life, and thus it makes sense that any knowledge he would covet would be related to magic.

-Is this safe to install mid-game?
Yes. If you have the sealed scroll in your inventory when you install this, you may have to drop the scroll and pick it back up in order for the mod to work.

-I don't like the buff you've created! Change it!
No. You're welcome to not use this mod.

-Do I need a specific book in my inventory in order to decrypt the scroll?
Nope. Just take it to the Arcanaeum. Rather than have you fuss about trying to locate a specific book yourself, the time looking for the book you need can be factored in to the time that passes when you decrypt the scroll.

-Why did you make it work like that?
I wanted this mod to be as lightweight and compatible as possible. I wasn't going to add a book to the Arcanaeum for that reason.

-Are the contents of the scroll in your mod canon?
Probably not, but I aimed to make them as lore-friendly as possible. I was not about to prove Anska right after she annoyed me in my current playthrough. :)

-Esl-flagged?
Yes.

For updating to version 1.0.1 on an existing save:

-If you do not have the buff yet in your save, no extra action required. Simply update and enjoy.
-If you do have the buff, input the following console commands after updating and loading your save:

1. player.removespell fe149803
2. player.modav magickarate -15
3. player.addspell fe149803

The issue was caused by me accidentally selecting "magickarate" instead of "magickaratemult" when making the magic effect. Sorry!