Magna Carta guaranteed English political liberties and contained clauses providing for a church free from domination by the monarchy, reforming law and justice, and controlling the behavior of royal officials. English barons demanded the king agree to the charter, as they were angry with his abuse of royal power.
A large part of Magna Carta was copied, (nearly word for word), from The Charter of Liberties of Henry I, which granted civil liberties to the English nobility.
Magna Carta was not considered a particularly important document during the medieval period during which the English crown power grew. Indeed, it is significant that in his historical play King John, William Shakespeare did not mention Magna Carta. However, Magna Carta became increasingly important in the 17th century as the conflict between the crown and parliament grew. As English society continued to grow and develop, Magna Carta was repeatedly revised, guaranteeing greater rights to greater numbers of people, thus setting the stage for British Constitutional monarchy.
Many later attempts to draft constitutional forms of government, including the United States Constitution, trace their lineage back to this source document. Numerous copies were made each time it was issued, so all of the participants would each have one. Several of those still exist and some are on permanent display.
Magna Carta is still part of English Law to this day. However, the only part that has not been repealed are the introductionary sentences, so it has no practical use and is retained only because it has been such an important historical document. Despite the fact that it has almost entirely been repealed, it is still used in arguments about reform of the jury system to this day.