Why might the english nobles have insisted on the right listed in number 45?

The Magna Carta is considered one of the most important cornerstones that set the principles of the democratic government.

The rights mentioned in point 45 were stated as follows:
"We will appoint as justices, constables,sheriffs, or bailiffs only such as know the law of the realm and mean to observe it well."

English nobles insisted on those right as those rights provided protection from any king who is a dictator or a tyrant and set guidelines to courts and justice that would decide the correct punishment for anyone who committed a crime. 

The answer is c because the law is facts