"I like the sword, of course!” Arthur said, laughing.

"Then you have made an unwise choice,” Merlin said. "The truth is not always clear. Certainly, the sword will make you a great warrior and help you win many battles, but it is the scabbard that has the greatest value. He who wears it will never die of his wounds.”

The reader can determine that the quote "The truth is not always clear” is a theme because

it sums up the elements of the story.
it is a main message in the story.
it sums up the conflict in the story.
it is an important event in the story.