What is the connection between “thinking and doing”?

The connection between thinking and doing is the chain of reasoning that humans are capable of.

From the text:

It sounds as if you supposed that argument was the way to keep him out of the Enemy's clutches. That might have been so if he had lived a few centuries earlier. At that time the humans still knew pretty well when a thing was proved and when it was not; and if it was proved they really believed it. They still connected thinking with doing and were prepared to alter their way of life as the result of a chain of reasoning.