Before the Magna Carta, Kings would taxes the people making them angry and wanting to go at war with the government. Kings would also completely control the decisions that Judges made in court. Kings could do as they pleased.
The noles have become angry at the king and decision to limit his power by making the magna carta. The Magna Carta is a document that makes it so the king has to go to the Parliament before making any decisions.
Parliament can now accept or deny the king's wishes. The king now also has to obey the Habeas Corpus which gives everyone a trail in court. Judges in court can now present evidence without worrying about the king's opinion.