How did western music change from the rise of Gregorian chant to the rise of the symphony? What are the biggest differences you hear?

How did western music change from the rise of Gregorian chant to the rise of the symphony? What are the biggest differences you hear? Who were important composers that led the various transformations, and what factors may have led them to be innovators?

Please note that this should be a fully-developed essay. Much of your overall performance on this assessment will hinge on the essays, so please spend plenty of time developing, writing, and editing your ideas.