Theory about the Rainbow Power

[ggg-2 3,552]

What if the Rainbow Powers are the ORIGINAL elements of harmony, the form they took before becoming the jewel like forms we know?

[Princess Lona 382]

That would make sense since the Rainbow Powers don't appear to have a physical form outside of the ponies themselves. Perhaps the Tree of Harmony is some kind of creator god and it created all of the abstract ideas required to create a peaceful society (honesty, kindness, etc) before it created the physical world. Once it started creating material things, it designed the Elements of Harmony to connect the raw power of those abstracts to the reality experienced by the physical life forms in that world. The Rainbow Power is the manifestation of the elements without a physical connection. It is pure, primal energy.

The box wasn't really holding the power in. It was presented as a way to teach ponies how to obtain a higher level of consciousness so that they could use the power. When the mane six all had their moments of clarity throughout season four, it was a form of training. The solving of each of their dilemmas created a deeper connection to their element within each of them. But it required Twilight's final realization to activate the full power.

[Duke of Canterlot 11]

I like this theory but what if I expanded it more

So the box came from the tree, meaning it has a conection with the elements, 

But what if it was a way of fusing the mane 6's personal magic with the tree's magic , similar to the elements of harmony but different at the same time, 

The elements of harmony were the magical esents of the 6 pillars 

Then it took a turn and found the mane 6 and changed slightly, (like how the element of magic cane from sorcerery)  but something that was mentioned in the show was that the elements were literally a part of the mane 6 symbioticaly conected to them symbioticaly,  

When they gave up the elements they gave up a part of themselves , so I guess the tree gave them the box to create their own elements. 

Part2

I think the idea of the box was a way for the mane six to create a new type of magic similar to the elements , 

The way they create this magic in my opinion , it is similar to creating magical artifacts,  they combined their own esents with that of the tree

Aka their items that turned into the keys and the box

By doing this they made a new type of magic similar to the elements which could be used to fight against evil once more

So in a way it is original ,  but only because it was new ,and belong to the mane six and not the 6 pillars 

Also it could be cutie mark magic , which I think would be able to use when a pony's personal magic aka the cutie mark magic is stored in something and grown or powered up , hence why it is shown in g5