Grand Master Schule:
Anyone wishing to become a Human Knight must have achieved at least level 20 and brought me the Sword of Ritual.
Your level is satisfactory, but you haven't passed the appropriate test. Speak with Sir Klaus Vasper of the Human Knight Guild. You should find him at the Warrior Guild in Gludin Village. Mind you, he's a stickler for proper etiquette, so be very polite!