Martin Luther King Jr in his "I Have A Dream" speech made use of metaphors to make his speech more effective, and this was one of those examples.
Here, he compares the legitimate anger of the African Americans and their agitation for equal rights to the heat of summer and freedom and equality as to autumn which invigorates.
He is calls the current time period a "season," implying that it will give way to a new season.
Explanation:
In this example, King refers to this time period as a "summer" of "legitimate discontent." By saying that the discontent is legitimate, King supports the idea that this period is significant in leading change against the discrimination of black people. Moreover, by saying that this is a "summer," King implies that a new season will follow this one, and that it will most likely be a season of more fairness and equality.
