Truly, Amir Mo’emenan Ali (Pbuh) is one of the servants of God who are selected by God, so honored and preferred above all others.
They are meant to carry the heavy responsibility of prophets after them; they are the vicegerents and successors of Messengers of God.
If there is a vicegerent to each prophet, Ali ibn Abi-Talib (PbuhI) is Muhammad’s vicegerent (Pbuh), indeed.
We know him superior to all other Companions since God and his prophet did; and upon this issue we have logical and referential evidence from books and Sunnat.
These evidences never will be the subject of doubts, because they are not only authentic and successively narrated before us, but also before Sunnite.
In this regard our scholars have written numerous books. And because the basis of Omavid government was held on the destruction of this truth and fighting and removing Imam Ali (Pbuh) and his sons, they ended up cursing his high personality in their sermons for the Muslim. They forced people to do the same, so the Shiit and followers of Imam Ali testify that he is the Wali of God,( i.e patron, friend and selected by God).
It’s not permissible if a Muslim curses Wali of God, and this was Shiite methodology to fight against oppressor government of the time;
In order to establish the dignity of God, his prophet and his believers;
To make a historical reference for all the Muslim of next generations, so they’d realize deeply the righteous status of Imam Ali (Pbuh) and the hideous position of his enemies.
In this way, our scholars made the move and advised testifying Imam Ali’s Walayat in Adhan and Iqama, as a rewarded (Mustahab) act, not an essential part of them.
So if someone repeats this phrase (testimony to Ali’s Welayat (Pbuh)) with the intention of an essential part of Adhan or Iqama, his Adhan and Iqama are abrogate 
6. It means that: it has been narrated many times so one can make sure it has been said by the Prophet (Pbuh)
7. Adapted from “then….I was guided” pp 88-89.