Illustration by Arthur Hughes, in George MacDonald - The Light Princess, in Dealings With the Fairies, Alexander Strahan (London), 1867.
It's interesting that MacDonald makes the King state an indubitable truth in strong terms, and then the sentence is finished off with the extreme of the King's objection, which, in that the latter is not generally true at all, lightens the whole thing. And that lightness perhaps helps the force of the first part of the sentence to penetrate, as there is no need any more for the automatic reaction of resistance or dissimulation which often occurs to such a definite statement. Thus it can make its impression without hindrance.
MacDonald himself seemed to like to play with words. The word light itself in the title of this book, would naturally be thought of with the meaning of opposite to darkness, until the story itself is known.