What does this line refer?

The correct answer to this is the triumph of Justice. Martin Luther King Jr. said this line in his famous "I Have a Dream Speech," which he delivered in front of the Lincoln Memorial in Washington, DC, on August 28, 1963. Dr. King hoped to inspire change to the economic and civil rights injustices in the country.

These specific lines are a reference to Isaiah 40:4, a verse in the Holy Bible, which goes, "Every valley shall be raised up,/ every mountain and hill made low;/ the rough ground shall become level,/ the rugged places a plain."