I don't know who the author of one sentence is worth ten thousand sentences because this sentence is not a novel or work that I know of. This sentence might be used to emphasize the importance or value of something. As for the meaning of this sentence, it might be an exaggeration to say that what someone or something said was very important and could even be worth a thousand words. It can also be used to describe something that is of great value or importance to make people value it more.