In a default WordPress install, jQuery is already called from its own library. The code above removes that and calls it from the Google CDN.
Keep in mind that whatever you add in functions.php, will be only for that specific theme. For better portability (and even more complexity….), put it in a plugin.
EDIT: sorry, this was a reply to a post that I thought was recent, but it wasn’t. It applied to the last post of page 1. Sorry!