If Sir Kael gets the holy grail and drinks from it he is immortal. If he gets wounds they are instantly healed....which MUST not happen since if he gets it he can build an immortal army who can never be defeated. The whole world will fall to them if they get it thought. They will wipe out more than 70% percent of the worlds population since for example they kill off women all the time saying they are "witches" which 95% of the teem isn't true..

Screenshot from The Last Resurrection (Hinph Gaming, 2001-2003)