Religion stems from misunderstanding; not being able to understand the world around us. Religion is unable to accept new information, information that contradicts a belief system. Religion stems from fear.
Rationality stems from understanding or wanting to understand; learning about the world around us in detail. Rationality allows us to accept new information, study it, and learn from it. Rationality is the ability to change our current understanding of the world when new evidence is presented. Rationality is the overcoming of fear.
And the allowance for there being things we do not know and may never know.
Religion on the other hand claims to know all and have explanations for all things (too bad it so often contradicts itself).