From the preview:
The primary purpose of a steelsoul protector is to serve as a shield against any harm intended for the priests of Cyriss. The shell of the vessel is engineered to be light enough to allow its bearer to move with startling speed while also being tremendously durable. The vessel’s frame possesses the strength necessary to employ the protector’s massive iron glaive to deflect incoming blows and deliver surprisingly swift counterstrikes. Only the most worthy members of the Convergence are afforded the tremendous honor of being chosen for soul transfer into one of these revered vessels.