The Grand Mufti of Damascus, Imam ‘Ala’ al-Dīn al-Haskafi, like other Islamic luminaries states in his famous Hanafi work Durr al-Mukhtār [The Chosen Pearl] written in the year 1070H:
“…The major (type) (i.e. the Caliphate) is the right of general administration over the people. Its study is in ‘ilm al-kalām and establishing it is the most important of obligations… ” [Book of Prayer, Chapter on Imāmah]
As the subject of ‘Ilm al-kalām addresses the proofs of beliefs, Imam Haskafi affirms the nature and scope of the Caliphate (Imāmah) within the Islamic sciences and elevates its rank as a foundational (‘aqīda) subject and not one that is merely a subject of Jurisprudence.
This is why so many classical works on creed comprise of sections on the Caliphate and its rulings. Imam Ghazali too in his essay on beliefs entitled al-Risāla al-qudsiyya fi qawā‘id al-‘aqā’id [The Jerusalem Epistle on the Principles of the Creed], as featured in his Iḥyāʾ ʿulūm al-dīn, states: ‘[…The people of truth] realized that expressing the devotional testimony “There is no god but God” [lā ilāha illa Llāh] is pointless and without benefit unless one completely comprehends the pillars and principles related to this testimony…Thus they came to know that faith is centred on these four pillars, each of which is centred on ten foundations.’
He then lists a summary of these pillars and foundations. The ‘fourth pillar of faith pertains to things known by transmitted reports, and has ten foundations’ including ‘the rulings pertaining to the Imām, the virtues of the Companions in their hierarchical order, the conditions of the Imāmah, and [to affirm] that even if a potential Imām does not possess piety and knowledge, his rule is valid if he fulfils the other conditions’.
Imam Ghazali concludes The Jerusalem Epistle with these words: ‘These, then, are the four pillars containing forty fundamentals which together constitute the principles of the creed. He who believes in them is in accordance with the people of the sunnah and distinct from the heretics’ [the translation from the Arabic quoted here is by Sidi Khalid Williams, The Principles of The Creed Kitāb Qawā‘id al-‘aqā’id Book 2 of The Revival of the Religious Sciences Iḥyāʾ ʿulūm al-dīn, Fons Vitae, Louisville, 2016, pp. 57-58, 89].
This therefore means that, for Ahl al-Sunnah, knowledge of the Imāmah (Caliphate) and its rulings is considered a foundational principle.
Another work on creed by Imam Ghazali is the book al-Iqtiṣād fi al-I‘tiqād, which includes a whole chapter on the Caliphate (Imāmah). In this section, he states ‘religion (dīn) and sultan are twins’ and he also presents what he describes as ‘definite legal proof’ (البرهان القطعى الشرعى) that appointing a caliph is an obligation. He states that ‘the obligation of appointing an Imām is among the essential requirements of the law [ضروريات الشرع] – a requirement that by no means can be ignored’. (To read more of the relevant excerpts from the book, see here).
The foundational nature of knowledge of the Caliphate is also mentioned by Imam Abu Mansur ‘Abd al-Qahir al-Baghdadi (d. 429H/1037CE) in his al-Farq bayn al-Firaq which is a major work on the beliefs of Ahl al-Sunnah. In this book, he discusses the views of the various heretical sects and contrasts this with the Orthodox position. Section 3 of chapter 5 of this book is entitled An Exposition of the Fundamental Dogmas (Uṣūl) Upon which the Orthodox (Ahl al-Sunnah) are in Mutual Agreement.
The following is excerpted from this section:
“The generality (jamhūr) of Orthodox Muslims (Ahl al-Sunnah wa al-Jamā‘ah) are agreed about certain principles (uṣūl) of the pillars (arkān) of the dīn, and a knowledge of the essence of every one of these is binding on every understanding, mature person…
As for these principles, the Orthodox are agreed about their basic character and they accuse of misguidance anyone who contradicts them…
The twelfth pillar (rukn) is knowledge concerning the Caliphate and Imāmah (and) the conditions of leadership…
Regarding the twelfth pillar relating to the Caliphate and Imāmah, they [the Orthodox] say that the Imāmah is a duty (farḍ) incumbent on the Community (Ummah), because the appointment of an Imām establishes judges and executives. He guards their frontiers, leads their armies, apportions the booty among them, and establishes justice for the wronged against the oppressor…”
So, according to Imam Baghdadi, knowledge of the Caliphate and its conditions is a fundamental pillar of the dīn.
[Cf. Moslem Schisms and Sects by Abu Mansur ‘Abd-al-Kahir ibn Tahir al-Baghdadi (d.1037) Part II: Translated from the Arabic with introduction and notes by Abraham S. Halkin, Porcupine Press, Philadelphia, 1935, pp. 171, 210]
In another of his books on creedal matters, Uṣūl al-Dīn, Imam Baghdadi devotes nine sections to the subject of the Imamate. He outlines the reasons why it is obligatory as follows:
“The general body [jamhūr] of the Sunnis, both theologians [mutakallimīn] and jurists [fuqahā’], together with the Shī‘a, the Khawārij, and most of the Mu‘tazila, hold the Imāmate to be compulsory [farḍ], that to set up an Imām and to submit to him are necessary, and that it is essential for the Muslims to have an Imām to execute their ordinances, enforce legal penalties (ḥudūd), direct their armies, marry off their widows, and divide the revenues amongst them…
Abu’l Hassan [al-Ash‘ari, founder of one of the Sunni schools of theology] argued that the Imāmate is itself an ordinance of the revealed Law, and though it can be demonstrated by reason that subordination to it is admissible, the necessity of it is known only by the authority of Revelation. Furthermore, the Companions (ṣaḥābah) were unanimous on its necessity, and in view of their unanimity no regard is to be paid to the opposition of isolated individuals. Again, the sharī‘ah contains ordinances which none can carry out except an Imām or a governor appointed by him, such as enforcing the legal penalties, giving in marriage women who have no guardians and establishing the jumu‘ahs and Eids. Even if the Community (ummah) were to act with perfect mutual equity, as al-Asamm [a Mu‘tazilī] postulates, yet it would still require someone to guard the property of orphans and lunatics, to despatch troops against enemies, and to carry out many other functions which only the Imām or a person appointed by the Imām can perform.”
[Cf. Lambton, Ann K. S., State and Government in Medieval Islam: An Introduction to the Study of Islamic Political Theory – The Jurists, Routledge, Abingdon, 1981, pp. 77-78]