How did the Black Death accelerate the pace of change in Europe?
The Black Death accelerated the pace of change in Europe simply because of the vast numbers of people that it killed.
It is estimated that the Black Death killed anywhere from 25% to 50% of the population of Europe in just a few years. Even if we take the low end of the estimate, that would be like 75 million Americans dying in a few years. That is more than the current populations of California and Texas (the two most populous states in the nation) combined. Not surprisingly, this would have a tremendous social and economic impact.
The major impact of all this death was that labor became more valuable. Before the Black Death, labor was plentiful. Feudal lords could easily keep tenants and serfs on their land because those people had no options. After the Black Death, there were jobs open in cities and there was land open because the people working it had died. All of a sudden, people who worked had leverage. This led to them taking more power. It also led to changes where peasants were no longer tied to the land but were, instead, allowed to work it in return for rent.
With these changes came much more struggle between the elites and the common people. This struggle accelerated the pace of social, political, and economic change in Europe.