The covenants were the chainlinks that bounded the Knights of the Round Table to the Emperor. There were a total of seven chainlinks that imprisoned the souls of the Rounds, and each of them signified an element of the Emperor's abilities.
One as such was Gladio, the covenant housing the Holy Swords that the monarch had bestowed to his knights. However, this particular chainlink didn't disappear the moment that it's used, a trait that was unique to it amongst the other six. Though it would gradually wear out the more often that the swords were called forth.
As opposed to Gladio's slow destruction, the others would instantly disappear. For instance, when the Emperor went berserk just at the moment, the covenant of Saeva disintegrated in an instant. Its vanishment inflicted the very agony that the Rounds were still experiencing.
