When Amir al-mu'minin heard the cry of Kharijites that "Verdict is only that of Allah" he said: 
The sentence is right but what (they think) it means, is wrong. It is true that verdict lies but with Allah, but these people say that (the function of) governance is only for Allah. The fact is that there is no escape for men from ruler good or bad.
The faithful persons perform (good) acts in his rule while the unfaithful enjoys (worldly) benefits in it. During the rule, Allah would carry everything to end. Through the ruler tax is collected, enemy is fought, roadways are protected and the right of the weak is taken from the strong till the virtuous enjoys peace and allowed protection from (the oppression of) the wicked