The importance of Skyward Sword
The reason why Skyward Sword is considered such an important addition to the Zelda series is because it answers so many questions which fans have been left with more or less since the series began.
It also needs to be noted that whilst it has been stated that it is not definite that Skyward Sword will remain as the first in the Zelda timeline the game still can be seen to serve as an origin story for items such as the Master sword and the establishment for characters like Ganondorf, Zelda and Link.
One of the most important question which the game answers is the mystery surrounding the origins of the Master Sword. The reasoning behind why the Master Sword is so much more powerful that the standard sword Link is stuck with was left more or less unexplained in previous games in the series. The bulk of the game follows Link questing to put the sword to its maximum capacity which is done by obtaining the various magaical components which give the weapon its power.