Without the power of the secular world, he could not wield any conventional authority. Without the crown and empty titles, it meant he could only bear his name with no other titles. He could not be a King, a Duke, or a Prince, and not even a Knight with any official title. Hence, every Starlight Knight had their own title except the bearer of the sword, who was always the Seventh Knight.
"Not fulfilling the above oath would lead to rejection by the Final Sword itself, but if it sought only personal virtue, why specifically restrict background and power? Are Princes and Dukes incapable of purity and kindness? And a King cannot be virtuous? Consider the vast sacrifices Orianna Cavon made, unable to maintain even a single subordinate or attendant, even renouncing her ducal title and hereditary rights!"