One supposes that it was the purpose of the old-fashioned coronation ceremony to impress upon the recipient his importance in a certain context, and of his acting henceforward on impersonal motivation in the best interests of the territory of which he now became the representative and agent, without being led astray by the merely personal.
According to Hans Herman Hoppe, in Democracy, The God That Failed, monarchs are better than democracies because monarchs own their territory and thus seek to improve it, while democrats can't resist the impulse to just spend as much as possible right now. Of course, kings can have as much as an impulse as anyone to spend everything now and forget about the future. Celia's explanation of the coronation's purpose has a similar, and true, ring to it; to impress on the monarch to care for, improve, and pass on his territory, rather than indulge in destructive levels of self-gratification.
Celia also notes 'divine right' in a way different from most:
And it is not irrelevant that the whole thing was supposed to place the royal person and his territory in relation to something outside of society, which was supposed to be run in accordance with a divine purpose. Cf. Land of Hope and Glory, frequently performed at coronations, "God who made thee mighty, make thee mightier yet".
This actually puts several bonds on the sovereign, rather than being some excuse for him to get to do whatever he wants. A warning that there is always a higher authority, and there are also always realms in which he is not sovereign- neither of these ideas is well understood by our government. Our officials seek to blanket the entire globe with regulations, and also reach down into the family and muck about there.