Why the monarch was the most powerful person in the middle ages?

Answer 1

"The Divine Right of Kings was the belief that legitimate kings were appointed by God and so were answerable to God alone."

Therefore, if God appointed a royal family to the throne, the monarchy would be second only to God according to the chain of being. That would make them the most powerful beings after God!

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The monarch was usually the most powerful person in a medieval kingdom or empire, but not always. There were times when the popes were more powerful than any monarch, but there were also times when someone else within the kingdom was most powerful. There were a few countries where the divine right was considered real, and there were others that did not adhere to the idea.

A good example of a king without power was King Childeric III of the Franks, who had very nearly no power at all. He was deposed by Pepin the Short, with the consent of the Pope, precisely because he had no power, and therefore had no reason to be king. Pepin later became king himself.