Reason for this semicolonn usage

Hi. I was looking at a quote by Martin Luther King Jr. online and saw this:

"Human progress is neither automatic nor inevitable. Even a superficial look at history reveals that no social advance rolls in on the wheels inevitability. Every step towards the goal of justice requires sacrifice, suffering, and struggle; the tireless exertions and passionate concern of dedicated individuals. Without persistent effort, time itself becomes an ally of the insurgent and primitive forces of irrational emotionalism and social destruction. This is no time for apathy or complacency. This is a time for vigorous and positive action."

In the third sentence, as to the use of a semicolon before the words "the tireless exertions," do we need it there (is it correct?). I think it is correct, but I want to hear your explanation. Perhaps, is it to make the sentence less confusing and more clear? Thank you in advance for your help.