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.

“Religion is a man. Finding that man and following that man. In the Bible, in the very beginning, it says that God was walking in the garden of Eden alongside Adam and Eve, and in the Quran it says that Allah blew from His spirit into Adam. After he blew from His spirit into Adam, he commanded the angels to prostrate down to Adam. What we get from this story is that there is this spirit, this part of God, the spirit of God that was blown, and it was sent inside creation. That spirit of God which was not born, nor does it ever die, and is everlasting, remaining in creation. That is God in creation. That is religion. To find the spirit of God and to follow it. The spirit of God went inside Adam, and then after Adam passed away (and Adam was just a veil), it went into his successor, and then his successor, and his successor, and his successor, and his successor, and is everlasting forever. So the spirit of God has many names and many veils. From his veils were Adam, Noah, Moses, Jonah and every single Prophet of Allah. All of the Prophets of Allah, they make up a part of God in creation, and God in creation is that spirit which is everlasting, from the beginning all the way to the end. The goal of religion is to find that man, that veil behind which the spirit of God is, and to prostrate. To obey. To give victory to him. That is religion.” - The Riser Abdullah Hashem Aba Al-Sadiq (From Him is Peace)

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.

“And when I have proportioned him and breathed into him of My [created] soul, then fall down to him in prostration." - The Holy Qur’an, Chapter 15 (Al-Hijr), Verse 29

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:

“Iblis said: ‘O God, pardon me from prostrating to Adam and I shall worship You like no other close angel nor Prophet Messenger has.’ God said: ‘I do not need your worship, but rather I want to be worshiped from where I want and not from where you want.’ But he still refused to prostrate, so God said: ‘Get out of it, you are impure, and verily upon you is My curse until the Day of Judgment.’” - Bihar Al-Anwar, Al-Allamah Al-Majlisi, Vol. 11, p. 141

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:

“Whoever dies and doesn’t pledge allegiance to the Imam of his time has died the death of ignorance.” - Al-Aql wa Al-Jahl fi Al-Kitab wa Al-Sunnah, Mohammed Al-Reyshahri, p. 275

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.

“O Messenger, announce that which has been revealed to you from your Lord, and if you do not, then you have not conveyed His message. And Allah will protect you from the people. Indeed, Allah does not guide the disbelieving people.” - The Holy Qur’an, Chapter 5 (Al-Ma’idah), Verse 67

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:

“Whoever I am the Master of, Ali is his Master.” - Mizan Al-Hikmah (Scale of Wisdom), Mohammed Al-Reyshahri, Vol. 1, p. 138

And the appointment of this man, Imam Ali (From Him is Peace) marked the perfection of the religion:

“This day I have perfected for you your religion and completed My favor upon you and have approved for you Islām as religion.” - The Holy Qur’an, Chapter 5 (Al-Ma’idah), Verse 3

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.

“Prophet Mohammed (PBUH & His Family) said to Ali (PBUH) on the night of his death, ‘O Father of Al-Hassan, bring me a pen and a paper,’ so the Messenger of Allah (PBUH & His Family) dictated his Will until he came to this position where he said: ‘O Ali, there will be twelve Imams after me and after them there will be twelve Mahdis. So you, O Ali, are the first of the twelve Imams, Allah the Exalted has named you in His heavens Ali Al-Murtada (the Content), Amirul Mo’mineen (the Prince of the Believers), Al-Siddiq Al-Akbar (the Greater Truthful), Al-Farouq Al-A’tham (the Greater Judge and Differentiator between truth and falsehood), Al-Ma’moun (the Trusted), and the Mahdi (the Guided). These names may not be attributed to other than you. O Ali, you are my vicegerent/guardian over my own family, their living and their dead, and upon my women: Whomever you kept, she shall find me tomorrow, and whomever you divorced, I am innocent of her, I will not see her and she will not see me on the Day of Resurrection. And you are my successor (Khalifa) over my nation after me. If death comes to you, hand it over to my son Al-Hassan, the righteous and benevolent. Then if death comes to him, let him hand it over to my son Al-Hussein, the martyr, the pure and murdered. If death comes to him, let him hand it over to his son, the master of worshipers, Dhul Thafanat (the one with hard skin on his knees) Ali. If death comes to him, let him hand it over to his son, Mohammed Al-Baqir (the Revealer of Knowledge). If death comes to him, let him hand it over to his son, Ja’far Al-Sadiq (the Truthful). If death comes to him, let him hand it over to his son, Musa Al-Kathim (the Patient). If death comes to him, let him hand it over to his son, Ali Al-Ridha (the Pleasing One). If death comes to him, let him hand it over to his son, Mohammed Al-Thiqa Al-Taqqi (the Trustworthy, the God-Fearing). If death comes to him, let him hand it over to his son, Ali Al-Nasih (the Advisor). If death comes to him, let him hand it over to his son, Al-Hassan Al-Fadhil (the Meritorious). If death comes to him, let him hand it over to his son, Mohammed the Safeguarded of the Family of Mohammed (PBUT). Those are the twelve Imams. Then there will be twelve Mahdis after him, so if death comes to him, let him hand it over to his son, the first of the close ones, he has three names, one like mine and my Father’s and it is Abdullah (Servant of God), Ahmed (the Praised), and the third name is Al-Mahdi (the Guided), and he is the first of the believers.’ ” - Ghaybat Al-Toosi, Vol. 1, p. 174; Bihar Al-Anwar, Al-Allamah Al-Majlisi, Vol. 53, p. 148

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).