He got up, took his mat and walked out in full view of them all. Christ's power flows from His authority. That's the nature of all legitimate power it is granted and guided by authority. When we read Rowling's series, we find that she effectively divorces power from authority. There is no sovereign person or principle governing the use of the supernatural.
Magical power is gained through inheritance and learning.
It is not granted by a higher authority, because there is no Higher Authority at least none higher than Harry's mentor, Albus Dumbledore, and the evil Lord Voldemort. The two are equal, antagonistic and unaccountable to a higher authority. In C.S. Lewis' Narnia , power and authority are welded together. That authority is Jesus, in the character of the great lion Aslan creator and sovereign ruler of Narnia, son of the Emperor Beyond the Sea. Good power is power that is bestowed by Aslan and exercised in accordance with his will.