Magna Carta

What is the significance of the Magna Carta, and where does it (the significance) come from? And especially the famous clauses (still valid today, though thought by some to be under threat in the name of national security):

(39) No free man shall be seized or imprisoned, or stripped of his rights or possessions, or outlawed or exiled, or deprived of his standing in any other way, nor will we proceed with force against him, or send others to do so, except by the lawful judgement of his equals or by the law of the land.
(40) To no one will we sell, to no one deny or delay right or justice.

72 words, 361 bytes (zips to 330), and more than* 800 years of context.
* because the context that led up to the granting of it in 1215 is as much part of its context as what happened since then.

(The full document, from the translation on the British Library site, is 4,537 words = 25,078 bytes, zips to 9,229 bytes.)