I haven't read the book. Can you elaborate on why the definite article is an important aspect of how the book is written or interpreted?

It's not the definite article per se. It's just that The Tortoise is specifically The Tortoise all throught the book, just as is in Lewis Carroll. Not getting that, I don't really believe anyone could have been getting the spirit of the book at all, no matter how all my downvoters may feel about it.