The rhetorical device that Reagan uses when referring to freedom in this passage is repetition.
Explanation:
When Reagan refers to freedom in the lines "Freedom leads to prosperity. Freedom replaces the ancient hatreds among the nations with comity and peace. Freedom is the victor. And now the Soviets themselves may, in a limited way, becoming to understand the importance of freedom" he repeats constantly the word Freedom, to emphasize the importance of this idea and make it more memorable for the audience.
