It's a Great Charter
Memorize the Magna Carta Day gives you the opportunity not only to learn about that famous document you heard about in history class but really know nothing about but also to actually read what it says.
How many other famous documents have you actually read?
You might know the preamble to the US Constitution, but that's about it, right?
Have you ever read the Constitution itself? You're not alone, if you haven't. I get the feeling that most Presidents and congresspersons haven't read it either. If they had, maybe (just maybe), they wouldn't break it so often.
Do you know who the last President was who didn't break a part of the Constitution? It might not have been one who was President in your lifetime. Really.
You can read a modern English translation of the Magna Carta here. It's okay to use this for memorization.
You can read the Constitution here.