What are the advantages of proofs of kingship like those listed below?
When the Greek hero Theseus is old enough to claim the throne of his father, the king of Athens, he pulls his father’s sword from beneath a huge rock. Sigurd's father, Sigmund, pulls Odin’s sword from a tree. Arthur becomes king of Britain because he pulls a sword from stone.
In each of these cases, the position of kingship is established based on supernatural proofs. These kings do not inherit their royal position from family - they perform extraordinary feats of strength, determination, and dedication that demonstrate their worthiness of the position.
When the king's position is confirmed by miraculous events, mere humans cannot ignore or refute the evidence. Sir Ector recognized the importance of the sword in Sir Kay's hand; he also recognized the need for Kay to be honest in attempting to claim the position for himself.
You are my son that I am proud of, and always will be, whatever you do. Will you promise me that you took it (the sword) out by your own might?" Kay looked at his father. He also looked at the Wart and at the sword. Then he handed the sword to the Wart quite quietly. He said, "I am a liar. Wart pulled it out.
Arthur's pulling of the sword from the anvil on the stone parallels the epic stories of other heroic leaders who arise from obscure beginnings to mythical accomplishments as leaders of their people. Based on the initial acts establishing their claim to the kingship, those positions were never challenged, not even by their enemies.