He held the tenet of the pre-existence of Christ's human soul. To the speculations in his "Apocalyptical Key" (1701) Fleming chiefly owes his posthumous fame. In 1793, and again in 1848, attention was directed to the apparent historical verification of some of his conjectures. He predicted the fall of the French monarchy by 1794 at latest, and fixed on a period around 1848 as the date at which the papacy would receive an ultimately fatal blow. Fleming follows Joseph Mede, but set the beginning of Antichrist at 768 AD. Fleming published:   Also eight sermons at funerals and special occasions between 1688 and 1716.