Is the imamate the most important matter of religion?

Ibn al-Mutahhar al-Hilli opened his treatise Minhaj al-Karama by stating that the imamate is the most important matter in the rules of religion and the noblest question for Muslims. Refuting this claim was the first thing Ibn Taymiyya did in Minhaj al-Sunna al-Nabawiyya. ^{1 2}

Al-Hilli calls his treatise "a noble treatise and a subtle discourse" containing the most important matter in the rules of religion and the noblest question for Muslims, namely the imamate. On it he builds the chapters of his book on the Imami school, the proofs of Ali's imamate and the Twelve Imams. ^{1 2}

Ibn Taymiyya answers in several respects. The first is that faith in God and His Messenger is more important than the question of the imamate. It is known by mass transmission, he says, that when unbelievers in the Prophet's time embraced Islam they were treated as Muslims and the imamate was never mentioned to them. ^{2 3} He argues from the agreed report that ties the inviolability of life to the two testimonies, prayer and zakat. He adds that the Prophet spared unbelievers' lives once they repented of unbelief, and that when he sent Ali to Khaybar he did not mention the imamate at all. ³

He then raises an objection: it may be said that the Prophet was himself the imam during his life, and that the imamate became the most important question only after his death. He answers that, even if this were true, it would make the imamate the most important question only at certain times and not absolutely, and that faith in God and His Messenger is greater at every time and in every place. ⁴ He states that the whole of religion is obedience to God and His Messenger, that obeying those in authority in what God commands is part of that obedience, and that this is why the foundation of religion is the testimony that there is no god but God. ⁵

Al-Hilli's statement here is taken from his opponent's quotation. The text of Minhaj al-Karama in an Imami edition has not yet been consulted, nor the positions of other Sunni schools such as the Ash'aris and Maturidis from their own books, nor academic studies of the question.