In a word, Renaissance is a burst of desires. People started to wonder. They gradually had the wish to see, to know, to understand things. The outcome is tons of fascinating works distributed in various fields of humanity.
Why there’s a burst? There are three reasons: 1. Christian suppresses people’s desire to stay in power. But Christian started to become inclusive started from Francis of Assisi. 2. The development of printing greatly reduced the cost to obtain knowledge, Christianity can no longer hold the knowledge to themselves. 3. European economy went prosper, people were no longer satisfied with sufficient food.
There were crises. Idealism once prevailed. Salvation in Christianity went all the way up when the plague swept Europe. History finally chose the current direction.