There are a lot of inventions that have changed one’s way of thinking. After the Roman Empire collapsed, those inventions were nearly lost, but there was a hope: the monks.
The monks were very sophisticated, they knew how to read and write. They had libraries of Greek and Roman books. The monks could have read about inventions such as the watermill. Then they built it and used it for themselves. The monks thought that the water was unsafe so they made beer instead. To make beer one has to crush up the ingredients. That can take awhile, but with the help of the watermill one could crush up the ingredients quickly and efficiently.
The watermill worked like this: the water turns the water wheel, which turns the connecting rod, which turns a gear, which turns a cam, which lifts whatever one wants.
So as one can see, the monks helped build the world because they were very smart and were able to keep a lot of inventions alive. So that is why people should thank the monks because without the monks the world would be a different place.