"Now is the time to rise from the dark and desolate valley of segregation to the sunlit path of racial justice. Now is the time to lift our nation from the quicksand of racial injustice to the solid rock of
brotherhood. Now is the time to make justice a reality for all of God's children. It would be fatal for
the nation to overlook the urgency of the moment. This sweltering summer of the Negro's legitimate
discontent will not pass until there is an invigorating autumn of freedom and equality."

What are the two pairs of contrasting images or ideas in the above paragraph?