Imam Ali (a.s.) was a model of justice at a time when the world was not ready to bear it. It was for this reason that justice has been greatly emphasized in the Nahjul Balaghah.
In Imam Ali’s speeches, sermons, letters, and short sayings, we see that in many many occasions he instructed the people to exercise justice as well as instructed the governors and his agents to apply justice and refrain from partiality, because, after the death of the Prophet Muhammad (S), people started again to do injustice and oppression was raising again, and it was because of Imam Ali's preaching against injustice and oppression that he was killed, thus removing justice and replacing it with oppression, which will continue until the day universal justice will be established.