Does the Magic stat affect all magic or only offensive spells

Spirit affects magic defense. Having more spirit lowers incoming magic attack damage.

One note from the wiki:

The player's overall Magic Defense was intended to be a sum of the character's Spirit stat and the MDef value of their armor, but due to a bug in the coding, the MDef value is not used and Spirit alone determines the character's Magic Defense.

Vitality affects physical defense. High vitality lowers damage from physical attacks.

EDIT: There's a full guide here (Thanks for the wiki link):

http://faqs.ign.com/articles/452/452504p1.html

Pasted relevant information:

?================?================?==========================?===============?
| Stat Name      | Purpose        | How Stat is Increased    | Stat Maximum  |
?================?================?==========================?===============?
| Strength       | Attack Power   | Power Sources            |       255 (+) |
|                |                | Gaining Levels           |               |
?----------------+----------------+--------------------------+---------------?
| Dexterity      | Speed (ATB)    | Speed Sources            |       255 (+) |
|                |                | Gaining Levels           |               |
?----------------+----------------+--------------------------+---------------?
| Vitality       | Attack Defense | Guard Sources            |       255 (+) |
|                |                | Gaining Levels           |               |
?----------------+----------------+--------------------------+---------------?
| Magic          | Magic Power    | Magic Sources            |       255 (+) |
|                |                | Gaining Levels           |               |
?----------------+----------------+--------------------------+---------------?
| Spirit         | Magic Defense  | Mind Sources             |       255 (+) |
|                |                | Gaining Levels           |               |
?----------------+----------------+--------------------------+---------------?
| Luck           | Critical Hits  | Luck Sources             |       255 (+) |
|                |                | Gaining Levels           |               |
?----------------+----------------+--------------------------+---------------?

The game requires Internet connection during the initial setup because of its DRM. After that, you can play offline if you wish. However, the way the game is programmed is that it always checks for connection and attempts to sync the save files to the cloud servers first. If it cannot find the connection, then it gives you the option to save locally.

It is a pain sometimes since a lot of times it would have problems connecting to their cloud server even though there is an internet connection. Many people have reported the "fail to sync" problem in game forums. Their cloud server is not very reliable for some reason.

The game still has a few bugs, but at least it does not crash on modern computers like the old one does (the old one runs on directx 5). The 3D graphics is cleaned up a bit and looks nice.