For those who beat the game. (Spoilers)

Did I miss something or did they never explain why Diamant, Ivy, Alfred, and Timerra are at the battle a thousand years ago? The beginning of the game, the Prologue cutscene, has Alear running through this grand hall where everyone is fighting with their Emblems. I've watched the full credits and still didn't get any inkling as to why they were there a thousand years ago.