What are the roles played in politics in the Middle Ages?

Society in the Middle Ages was organized into three roles or "Orders:" the bellatores, laboratores, and oratores. Or, those who fight, those who pray, and those who work. The nobility made up the class of bellatores, or fighters. The laboratores class was made up of the peasantry or commoners who worked the land owned by the nobility. The clergy, or religious community, were the oratores, whose duty it was to pray on behalf of the community to maintain peace with God.

As I mentioned before, there was a relationship between the nobility and peasantry, which we call the feudal system. In a kingdom, the land might be divided up among the knights or friends of the king who constitute the nobility. In return for the land, nobles were obligated to provide military service. The land held by nobles was further divided up among his vassals, often lesser nobles in society. Here, too, military service was the "payment" for the land. These lower-ranking nobles then had a relationship with the peasantry, who lived on and worked the land. 

The oratores, or clergy, existed somewhat outside of the feudal relationship. Clergymen and women might come from either nobility or peasantry, and sometimes served to negotiate the relationship between the two. Peasants did not have much say in political matters as they did not own land or control their means of production. Political decisions were primarily made by the land-holding nobility, as long as these decisions did not go against the laws or wishes of the King.