What is the meaning of "after he was not so" in Ibn Kathir's statement about the Mahdi: "Allah will rectify him in a single night," meaning "He will accept his repentance, inspire him, and guide him, after he was not so"? And what about the Mahdi's name and birthplace?

The Mahdi's name is Muhammad ibn Abdullah, and he is a descendant of Fatimah. He will be born at the end of time, near the Hour. Ibn Kathir's statement means that Allah will favor the Mahdi by teaching him, guiding him, and granting him success. He will repent in a single night, or his affairs will be rectified and his status elevated in one night, during which the people of influence and authority will agree upon his caliphate.