What Renaissance? The Carolingian renaissance? What do you see as the "setting free mankind to think" as opposed to what came before?
Don't fall for the idea that the Middle Ages were the Dark Ages (a term first used by Gibbon).
During the Middle Ages people like Dante Alighieri and Bede lived. The great art of the Gothic period was present and scientific discoveries. What makes you think that mankind suddenly started discovering thinks anew?
Firstly you are wrong to say "mankind" as the Renaissance never affected the Greek world which had the same as before. It never went to the Islamic lands or India or China
What new thinking do you see in the 1400s that people didn't think in the 1300s?
'The Renaissance was a cultural movement. It was the revival of learning based on classical sources, the rise of courtly and papal patronage, the development of painting perspective, and advancement in science. It spanned from the 14th to 17th century and started in Italy..https://www.answers.com/Q/What_was_the_date_of_the_renaissance
The advances in art were quite significant. Realistic perspective, both single and double vanishing point, naturalistic depiction of human form, recovery of knowledge of ancient sculpture, first large dome raised in the west since Antiquity.