In Dylan's poem "Blowing in the Wind," what is meant by the lines "How many times must a man look up/Before he can see the sky"?

Bob Dylan's song combines the romantic and the political quite beautifully. The two strands complement each other in the song. In these lines, Dylan comes back to the central question of what does it take to be human, which he keeps repeating in different forms throughout the song. He examines the values of human experience, the limits to human tolerance, indifference and habituality, before it all breaks free in the revolutionary upsurge--" How many years will it take till we know/That too many people have died".

These questions are rather unanswerable and the answer will always be blowing in the wind. In the lines quoted in the question, Dylan questions the onset of intuition, sensibility and awareness in temporal terms. How many occasions does a man need to arouse his sense of insight into his own social responsibility. However, at a more individual level, the lines may also refer to the timing of epiphanic knowledge. The following lines make the sense clear--"How many years must one man have/Before he can feel, he can cry". This is a clarion-call to man's waning sensibility at the wake of social disasters.