In 1215, the nobles demanded for King John to lose power, by writing 63 rights that nobles thought they deserved.
The nobles wrote the Magna Carta to decrease the power of the king and to declare their rights. They were trying to accomplish more freedom and less self government.
You wont have all the power for long!!
The nobles now have more rights and freedom!
In the end, the document lowered the power of the king and gave more rights to the nobles. Things changed by the people getting more freedom, than before. King John was not able to take all the power for himself anymore.