What is the reasoning behind sending an infallible Imam?

Question: What is the reasoning behind sending an infallible Imam (pbuh) to preach/decide on belief/faith and not preach/decide on Jurisprudence, given the fact that the Islamic Nation (Ummah) requires the worldly rulings of Jurisprudence more?

Answer:
Imam Al-Mahdi (pbuh) walks in the footsteps of his grandfather the Messenger of Allah (pbuhap) and in the footsteps of the Prophets and Messengers (pbut) and does not go beyond that to anything else from the footsteps of the wicked people from the corrupt scholars, so if you re-examine the footsteps of the Messenger of Allah (pbuhap) and the footsteps of the Prophets and Messengers (pbut) then you will find at the start of their Message they started with the belief/faith and Monotheism in particular, then they shift towards legislation/Shari’a or Jurisprudence, so the example of the ‘belief/faith and Monotheism’ relative to the ‘legislation/Shari’a and Jurisprudence’ is like the example of the foundation and the walls to the roof, so the roof cannot be built until after the foundation and walls are built.

And now if we re-examine the dispatch of Moses (pbuh) by his grandfather he (Moses) called/invited to the belief/faith and monotheism until he (pbuh) spent forty years in Egypt inviting to the belief/faith, and even after Egypt (i.e. after the crossing river) he spent a long time inviting to monotheism and the reformation of the belief/faith with the children of Israel, and he did bring the Jurisprudence until after a long time when he went to His Lord’s (appointed) term during the ‘confusion’ (lasting 40 years, Quran {5:26}), and the Quranic verses were explicit in saying that when he returned from His Lord’s (appointed) term he was carrying the inscribed tablets of Legislations/Shari’a, so what was he acting on before coming with the Legislations/Shari’a? (Nothing) except that he was spreading Monotheism and the true belief/faith, the Al-mighty said: {When Moses came back to his people angry and grieved, he said: “Evil it is that ye have done in my place in my absence: did ye make haste to bring on the judgment of your Lord?”? He put down the Tablets seized his brother by (the hair of) his head, and dragged him To him. Aaron said: “son of my mother! The people did indeed reckon me as naught, and went near to slaying me! Make not the enemies rejoice over my misfortune, nor count thou me amongst the people of sin.”}[1].

As for Muhammad (pbuhap) he invited/called during thirteen years in Mecca and it was mostly for the reformation of the belief/faith and Monotheism and he did not extend (the call) for the reformation of the legislations (Shari’a) until after the thirteen years of the Call, and Imam Al-Mahdi (pbuh) doesn’t leave the Tradition (Sunna) of the Messenger of Allah nor the Tradition (Sunna) of the Prophets and Messengers, indeed it is the Tradition (Sunna) of Allah from the past and (for) the future and you will not find a change/variation to the Tradition (Sunna) of Allah.

Furthermore O my dear brother observe through investigation and contemplation that the Legislation/Shari’a in every religion is as much as the (amount of) Monotheism in that religion, so the Islamic Legislation (Shari’a) is more complete than the previous Legislations (Shari’as); because the Monotheism inside the Quran and that was clarified in the past by the Messenger of Allah and the preceding Imams (peace and blessings be upon them) is more complete than the Monotheism that was brought by the preceding Prophets and Messengers, so O my dear brother if you knew from Ahlulbayt (pbut) that all of what the Prophets and Messengers came with of Monotheism was 2 pieces, and nothing was propagated among the people except the 2 pieces, and that Imam Al-Mahdi (pbuh) will come with 25 pieces ([2]) of Monotheism and the information is (gained) through the path of the Heavens and what is inside them and the true belief/faith that pleases Allah, and he will propagate among the people 27 pieces that are the complete Divine Monotheism that Allah sent Muhammad (pbuhap) with, however there hasn’t propagated in that time from him (those 27 pieces) except 2 pieces (and) it is known that the Legislation/Shari’a that Imam Al-Mahdi (pbuh) will come with is a lot larger than what is found among our hands right now; because the Islamic Legislation/Shari’a right now is on the (same) amount of the 2 pieces only, is it possible that Imam Al-Mahdi (pbuh) propagates 27 pieces of Legislation/Shari’a before he propagates 27 pieces of Monotheism, which the Legislation/Shari’a is built upon?

Certainly the answer will be no; so for the many reasons I have explained and clarified the people can’t bear the 27 pieces of Legislation/Shari’a unless if they (believe in) monotheism of Allah through the 27 pieces that Imam Al-Mahdi (pbuh) is assigned with spreading and propagating it among the people, and praise is to Allah alone.

[1] The Holy Qur’an: Surat Al-A’araf {7: 150}.
[2] From Al-Sadiq (pbuh): (“Knowledge is 27 letters and the entire amount that the Messengers came with was 2 letters and the people don’t know other than these 2 letters even until this day, so if our Qaim rises the 25 letters will come out and he will propagate them to the people and he will join the 2 letters with it so that he can propagate 27 letters”) Bihar AlAnwar: vol 53, page 3.

Question 120, page 188