The Sealed Statues were a safeguard prevented anyone one from accessing the Temple of the Sacred Sword which held the Master Sword in its Sacred Pedestal that was keeping the final Soul Fragment of Spirit of Evil's soul under seal. While presumably designed to protect the Temple from evil, this made it difficult for Princess Zelda and her Hyrulean Forces to access the Temple when they went to retrieve the sword in order to use its power to stop Cia and her Dark Forces. Fortunately, Zelda reveals that their allies from across the ages possessed the ability to awaken the three Sealed Statues. Activating each statue required Link and the rest of the Hyrulean Forces to protect their allies while they activated each statue. After all three statues were activated then the door to the Temple will open.
Statue of Servitude
Located south of the Temple in the Town Entrance Keep, the Statue of Servitude required either Impa or Fi (if Impa is controlled by the player). Apparently it required the power of one who lived to serve others (like Impa who lived to serve the Royal Family of Hyrule and Fi the Spirit of the Goddess Sword who was created to serve the Goddess' chosen Hero).
Statue of Twilight
Located near the Temple in the North Square Keep, the Statue of Twilight required either Midna or Agitha (if Midna is controlled by the player). Apparently it required the power of one who lived in the Era of Twilight.
Statue of Wave & Flame
Located near the Temple in the South Square Keep, the Statue of Wave & Flame required either Darunia or Ruto (if Darunia is controlled by the player). Apparently it required the power of either the Sage of Water or Sage of Fire.