Chest of Harmony and Season Finale Theory

With what I've read on tvtropes.org, it sounds like the chest is pretty much their version of Pandora's Box. It'd make sense given the series' Greek motif.

This is what I think happened:
A thousand years ago, Celestia and Luna came upon a box. Not knowing what was inside, the two open it up, letting loose all the horrors that continue to plague Equestria.

The box may have also produced the Tree of Harmony and the Elements of Harmony. The two decide to use the elements to try and fix what they've done.

Fast forward to today. Twilight Sparkle is a new princess of Equestria. Celestia is appointing her a kingdom to rule over, which is currently being controlled by a terrifyingly dangerous adversary and they hire Discord to help stop it, much to Twilight's dismay. The chest supposedly plays a key role (no pun intended) in stopping the finale's big bad. If you think back to the tale of Pandora's Box, the only thing left was Hope. I'm not suggesting that when the box is reopened, everything will be a-okay, but it might knock the big bad down a peg.

If you go back to the episodes where everyone got their keys (Twilight has yet to acquire hers, probably will in the finale), they were without hope: Rarity's friend stole her fabric; Rainbow Dash was torn between flying with her Ponyville team and the Wonderbolts; Pinkie Pie assumed the town didn't need her when Cheese Sandwich showed up; Fluttershy almost made the Breezies miss their chance at going home and had to give them the boot and Applejack was down in the dumps after she admitted to lying and even encouraged Flim and Flam's deceptive tactics. Each of these events were brought on by them in some way, slightly or majorly.

It's just a theory though. Thoughts? Questions?