Why was the Fatimid missionary organization like a branch of government?

The Fatimid missionary organization, known as the da'wah, functioned as a third branch of government alongside the military and bureaucratic establishments because it was an elaborately and secretly organized network that served as an institutionalized state religion.1

Under the supreme direction of the chief missionary in Cairo, this network operated across lands still under Abbasid suzerainty to gain converts for the Isma'ili faith and recruit workers for the Fatimid cause. The mission was essential to the Fatimid grand strategy against their Sunni rivals, as it was tasked with preaching and practicing subversion against the Abbasid order. By formulating and disseminating Isma'ili doctrine, the mission provided the intellectual and theological arguments necessary to challenge the Abbasid claim to the caliphate and assert the Fatimid ruler's position as the true imam and spiritual head of the Isma'ilis.1