The traditional medieval view of the world was divided into social classes. Through early and peak feudal era, the society had three classes: one that ruled (nobles), one that pray and care for spiritual and social needs (clergy), and one that does real work (the land bound peasant). This system had worked as long there was not large urban class that had a lot of money. Through the peak and late feudal era, the importance of the cities grew, they became more powerful, wealthier, and harder to control by ruling elite. When cities reached tens or even hundred thousands of population (like Paris, Venice), they changed the social, political, cultural, and economical fabric of the medieval society.
Cities were not bound to land, but to commerce. Almost all merchant and craftsmen had education in order to conduct business transaction, which undermined the intellectual supremacy of the church. Besides, the rise of the guilds and social services within cities decreased the dependence on church alone. Educated urban class traveled for business, created capital, and when it earned money, it decided what is good for them. The did not care what the church said about luxurious life on Earth for exchange of better prospect in a Heaven (increasing living standard was seen as obstacle to be saved), nor were interested to share its wealth with nobility. Through the 14th century, the shift and emphasis on money and capital instead salvation within the church doctrine became prevalent through much of the Europe. People seen that church was unable to save urban class from plagues, so its prestige declined. People who conducted business invested money back into economy and build mills, breweries, wool and silk industries. One of the origin of the modern capitalism lies within the economic shift that occurred between 1330-1400. The unequal distribution of wealth also gave rise to some very popular urban revolts that were unheard prior Black Death.
Through the late feudal era, while population of Europe declines, the cities continued to grow, and lured people from countryside with better economic prospects and more personal freedom (you were not bound to labor for feudal). People could travel farther (especially for trade and market fairs) and interaction with different cultures many of them non-christian opened mind to many new ideas. Through early renaissance, the idea of tolerance and respect was seeded through the turbulent 14th century. People were educated in one of the tens of new universities and hundreds of schools often rejected dogmatism of the church, and rediscovered ideas of antiquity that was hidden by clergy for 1000 years. Once the pillar of feudal Europe, the Church, was removed, this three way cast system collapsed.