“Take my place among my people.” [Surah al-A‘raf 7:142] This was because Moses—peace and blessings be upon him—had gone away for his appointed meeting with his Lord.
However, the first view is correct: it is permissible to say “the successor of Allah,” because Allah has appointed him as a successor over His servants so that he may establish His justice. This does not mean that Allah Most High is absent. Rather, Allah is above His Throne and knows everything. There is a difference between Moses appointing Aaron as his successor and Allah Most High appointing this caliph as a successor on earth.
Those who say that it is not permissible argue that one says, “the successor of the Messenger of Allah, peace and blessings be upon him,” because he has succeeded the Messenger of Allah among his community in knowledge, action, calling to Allah, and governance. That is, the caliph must succeed the Messenger of Allah, peace and blessings be upon him, in these four matters: knowledge, action, calling to Allah, and governance. The caliph’s responsibility, then, is no light matter.
As for knowledge, it means that he must be knowledgeable of the Sharia. This is why the caliphs during the era of the righteous early generations were scholars. If he is incapable of this, then he must have close advisers who are knowledgeable of Allah’s Sharia. These advisers must also be acquainted with the conditions of the age and able to relate contemporary developments to the principles of the Sharia. For some people may be scholars, yet have no knowledge of people’s circumstances or of the demands of the age. You find such a person wishing to impose what he knows without considering reality, and this is an error. Rather, in addition to his knowledge, the scholar must be an educator: he must consider reality in order to apply it in accordance with the principles of the Sharia. We do not mean that he should consider reality in order to twist the principles of the Sharia to fit it; rather, he should bring reality into conformity with the principles of the Sharia,