Many of the Islamic teachings and religious precepts have been changed by wrong interpretations and explanations. The factor behind these changes and distortions are the malicious motives and mean desires of people and governments, who in the course of history, have paved the way for establishing their authority and opening the path of playing with religious creed and realities. The ‘Ghaibat’ (concealment) of the ‘Hujjah’, who is the genuine interpreter of Qur’an, has turned into an appropriate opportunity for the wrongdoings. Distortion of most of orders began just after from the holy prophet’s era and would continue till the time of ‘Zuhoor’. One of the vital steps of Hazrat Mahdi would be his campaign against distortions and wrong interpretations that have kept the human mind engaged for centuries.
Thus, his religion would not be different from the religion preached by the holy prophet (s.a.w.a.). Rather, it would be a return to the logic of pure and true original Islam and the same heavenly and everlasting Book.
As such, in numerous instances, it would differ with what people used to practice in the long history. During ‘Ghaibat’ (concealment), its likely people haven’t acted upon the true Islam and some have even interpreted wrongly Islam and Qur’an so much so that at the time of ‘Zuhoor’, people will imagine that Hazrat has brought a new creed.
In many traditions it has come down that Hazrat would give a new start to Islam:
“ يستانف الإسلام جديدا…..”
Similarly, it has come down in the holy Qur’an:
“And to Him shall submit whoever is in the heavens and the earth, willingly or unwillingly.” (Qur’an, 3:83)
This verse reveals that Islam and monotheism would turn widespread; the holy prophet’s Islam and the Qur’anic laws would be implemented. Most of the sciences too would follow the realities and Hazrat would explain and interpret truly the verses of Qur’an and divine rules.
While talking about Mahdi’s ‘Zuhoor’, Amir-ul-Mu’minin (a.s.) says about Hazrat’s reforms as follow:
“After replacement of Allah’s worship with capricious desires, He shall restore worship of capricious desires with worship of Allah. After restitution of Qur’an with personal opinion and understanding, he shall restore Qur’an in place of personal judgements and opinions.” 
Imam Sadiq (a.s.) says as well:
“…when our Qaem rises, everyone would set forth before him reason from Allah’s Book and they would interpret and explain Allah’s book (Qur’an)…” .
The wrong interpretations and explanations of Qur’an is the problem Hazrat Mahdi (a.t.f.s.) would face during ‘Zuhoor’. These distortions and personal views would turn upside down the divine book and sunnah till the time of ‘Zuhoor’ to such extent that Amir-ul-Mu’minin (a.s.), in continuation of the aforesaid sermon interprets the divine book and Sunnah as dead:
“He (Mahdi during ‘Zuhoor’) shall give life to the dead Book and Practice of the holy Prophet…”
Therefore, during the time of ‘Zuhoor’, Hazrat Mahdi (a.t.f.s.) would cast aside the decorations put on divine religion and precepts, and remove all sorts of distortions and interpretations levied against the Qur’an and religion. He shall establish monotheism and Qur’anic justice in the human society. He would gather the whole world under one banner, one creed, one heavenly book (Qur’an) and one doctrine. He would set up one nation from the human society.