In the society of the High Middle Ages, social classification of the people who were not leaders or privileged members by birth was determined by your profession. While I do not believe this is moral or just, this society was divided into three classes. The highest class was people who fought and defended their country. The next class of society was people who were involved in the spiritual lives of the people. The lowest class was people who worked for those who had money or power.
Knights or those who fought were young nobles that were part of an elite class. The first step to becoming a knight was being a paige where you learned basic training. The second step was being a squire where you learned more of how to battle and got to test your skills against each other. The third and final step was becoming a knight which ended your basic training and then you helped defend the country. Training was in arts of war, learning to ride and manage horses, acquire skill in wielding a sword, being able to hurl a lance, shoot with a bow and arrow, and care for their armor and equipment. Trained for war, nobles often devoted a considerable time to fighting and intergenerational quarrels were common. Knights were in the top classification because they were the protectors of the people who had power and responsibility. The people in power did not want to lose their privileges and property.
The monks and nuns in this period provided for the spiritual needs of those in power. Religion was a very important aspect of the period. Many monks were given to the monastery as children by their upper class families. Women had few career choices during this time. If they were not serfs, they either stayed home or joined the convent. Women were also given by their families to the convent as were the monks. Monasteries served as cultural centers and played a significant role in the social life of the aristocrats.