Quran

Allah's Messenger was already a human right activist [research Hilf ul Fudul - the Pact of Benefit]. 

This is proven through the statement of Khadija, who said to him; you help the orphan, oppressed, needy etc.
Allah's Messenger would wish that he could get rid of humanity's problems, because no matter how much he tried to support the oppressed - the corruption in society only increased. 

So Allah gave him a message which would provide a perfect guidance as a connection between Allah and His slave, and the perfect guidance between man and society.  

Rasulullah s.a.w had hardly any political power because he was an orphan, and his own uncles were his worst opponents, so even his powerful tribe could not support his message. All he was in the sight of people is that he is an honest businessman.So Allah tells him; Read with the Name of your Master. So the people know that you are not saying they are your own words.  

-source: Tafseer al-Alaq by Nouman Ali Khan