The most difficult struggle is the one against hypocrisy, for it is the struggle against the cunning who use the stupid as their weapon. This fight is several degrees more difficult than the fight with unbelief, because, in the battle with unbelief, the struggle is against an unconcealed, open and unhidden current, while the struggle against hypocrisy is in fact a struggle against concealed unbelief. Hypocrisy has two faces: one is the outward, face - Islam and Muslim; the other inward - unbelief and evil. It is very difficult for the ordinary people to spot this latter aspect, and sometimes impossible; and thus the struggle with hypocrisy ends in failure because the great majority of people cannot extend the reach of their perception beyond outward forms and the hidden does not become apparent. They do not have a long enough range to penetrate the depths of the inward nature of things.
Amir al-mu' minin (as) wrote in the letter he sent to Muhammad ibn Abi Bakr
The Messenger of Allah said to me: "I do not fear for my community from the believer or the unbeliever. As the believer, Allah will protect him because of his belief, and, as for the unbeliever, Allah will humiliate him because of his unbelief. But I fear about everyone of you who is a hypocrite in his heart and learned in speech. He speaks what you can accept, but he does what you cannot accept. 
The Prophet here points out the danger in hypocrisy and the hypocrite, because the majority of people are uninformed and unaware, and are taken in by outward appearances. 
Care must be taken over the fact that with every bit that stupidity increases, the way opens further for hypocrisy. The struggle with the stupid and stupidity is the struggle with hypocrisy too, for the stupid are the tool in the hands of the hypocrites. Naturally, the struggle with the foolish and with foolishness is to disarm the hypocrites, and take the sword out of their hands.
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. ibid., Letter no.27.
. Thus we see throughout the history of Islam that every time a reformer arises on behalf of the people to reform the state of their society and religion, and the interests of the unjust and the profiteers are endangered, these latter immediately don the disguise of sanctity, and display their piety and religion.
When al-Ma'mun ar-Rashid, the `Abassid Caliph famous in the history of rulers for his epicurianism and extravagance, saw that the `Alawis were on the ascendence, he put on a change of clothing and showed himself in public in a new light. Then Abu Hanifah al-Iskafi, who neither took a penny from him, nor benefited from him, praised him for this and composed the following panegyric:
O Ma'mun, the like of whom among the rulers of the State of Islam
Has never been seen, by Arab or by simple peasant,
Wore a coat of fur for so long
That it became old, worn and tatty.
His close companions were amazed at this excess
And asked him for the reason for this.
He said: "Tales are left behind by kings
Among the Arabs and the non-Arabs, not by fine cotton and linen! "
And so on, each in his way excelling in the well-tried and oppressive politics of "holding the Qur'an up on spears", and defeating all effort and self-sacrifice, nipping each new resurgence in the bud. This is nothing but the ignorance and unknowing of people, which does not know how to distinguish between slogans and reality, thus closing the way of resurgence and reformation to themselves, and then realising that all the preparatory work has been cancelled out and that they must start at the beginning again.
Of all the great points we learn from the life of 'Ali, we see that this kind of struggle is not confined to any special group, but that everywhere that a group of Muslims, or those who are got up in the garb of religion, become a tool for the advance of non-Muslims and the progress of colonialism, and the colonialists, for the protection of their own interests, give them cover, and then use them as their shield, so that it becomes impossible to fight them without doing away with the shields, then it is necessary to begin by fighting with these shields and destroying them so as to remove the obstacle in the way and be able to attack at the heart of the enemy. Perhaps the machinations of Mu'awiyah had something to do with the Khawarij's sabotage, and therefore even on that day Mu'awiyah, or at least people like al-Ash'ath ibn al-Qays, and other elements in the sabotage and disturbances, gave cover to the Khawarij.
The history of the Khawarij teaches us the fact that in every resurgence the "shields" must first be got rid of and the fools fought with, just as 'Ali, after the events of the arbitration, first of all attacked the Khawarij and then intended to follow upon the tracks of Mu'awiyah.