An absent Imam creates a practical problem that has shaped Twelver Islam more than any other doctrine. If religious authority belongs to the Imam and the Imam cannot be consulted, who decides?
The answer developed over centuries. Authority passed to the scholars, the ulama, as general deputies of the hidden Imam. The Usuli school, which prevailed decisively over its Akhbari rivals in the eighteenth century, holds that a qualified jurist may exercise independent reasoning, ijtihad, and that ordinary believers must follow a living jurist, choosing a marja al-taqlid, a source of emulation, whose rulings they observe and to whom they pay religious dues. Akhbaris had held that the traditions of the Imams suffice and that such reasoning is illegitimate. The Usuli victory gave Twelver Shiism a living, funded, independent clerical hierarchy of a kind Sunni Islam does not possess, centred on the seminaries of Najaf and Qom.
The extent of that authority is contested within the tradition. Ruhollah Khomeini argued that the jurist's deputyship extends to political rule, wilayat al-faqih, and the Islamic Republic of Iran was built on it after 1979. Many senior Shia jurists, including the most widely followed authority in Najaf, hold a narrower view in which the clergy guide but do not govern, and the quietist position has substantial support in Iraq and elsewhere. This is a live argument about the meaning of the occultation, not a settled doctrine.
The messianic charge also cuts both ways politically. Because the Imam's return will establish justice, any existing government occupies a provisional and in principle illegitimate position, an idea that has fuelled both revolutionary movements and a tradition of political withdrawal, depending on who was drawing the conclusion.