Peasants were at the bottom of the Feudal System. They worked on the manor's farm and payed taxes in return for their knights protection. Questioning your place in this society was frowned upon. Feudalism was the ultimate control for medieval society.
GET TO WORK PEASANTS!
The Black Plague was the biggest epidemic in Medieval Europe as millions of people died and there was no cure. This shook the cultural foundation of faith and caused Feudalism to fall.
The gravitation towards cities and the growth of population increased the need for trade and a more skilled, educated workforce.