Religion is a man
The only religion that is acceptable to God is submission. The people are expected to be in a constant state of complete obedience and submission to God no matter what, in good times and in bad times, in sickness and in health. But how do we submit ourselves to God? How is that done?
Humans do not have a direct communication with God, so mankind has no idea what God wants from them, unless God sends someone as a messenger or as a representative from himself.
When God created Adam (PBUH), he wanted that the angels and creation as a whole prostrate and submit themselves to Adam (PBUH), that is how God wanted to be worshiped.
Iblis (May God curse him) however refused to prostrate and was counted amongst the disbelievers in a Hadith by Imam Al-Sadiq (From Him is Peace) the Imam makes it clear that the prostration of Adam (PBUH) was the only way God wanted to be worshipped:
The first one who compared and was prideful was Iblis, and pride is the first act of disobedience to God. He said:
Prostration and submission to the spirit of God in every day and age is religion. You can die as a so-called Muslim believing in the Prophethood of Prophet Mohammed (PBUH & His Family) but if you reject his successors you will not be counted amongst the believers.
Prophet Mohammed (PBUH & His Family) said:
This means that Prophet Mohammed (PBUH & His Family) was not the last guide for mankind, God would never cut his ties with creation through a man after he has established that his religion is through a man. That is why the verse from the Qur’an came down insisting him to reveal his successor otherwise it would be as if he had done nothing.
It was at that moment that Prophet Mohammed (PBUH & His Family) on the day of Ghadir Khum took the hand of Imam Ali (From Him is Peace) saying:
And the appointment of this man, Imam Ali (From Him is Peace) marked the perfection of the religion:
On the night of his death, Prophet Mohammed (PBUH & His Family) reaffirmed his successorship to Imam Ali (From Him is Peace) and listed the successors that would follow after him, infallible guides that would point to the right path in every day and age.
Today, the one who houses the Spirit of God and the one who must be obeyed without negotiating is the Mahdi mentioned in the Will of Prophet Mohammed (PBUH & His Family), the “Abdullah” mentioned in the Will, and that man is Abdullah Hashem Aba Al-Sadiq (From Him is Peace).