What was the source of inspiration for Michelangelo Buonarroti's painting Last Judgement? What does the painting depict?

It is a depiction of the Second Coming of Christ and the final and eternal judgment by God of all humanity. The souls of humans rise and descend to their fates, as judged by Christ surrounded by prominent saints including Saints Catherine of Alexandria, Peter, Lawrence, Bartholomew, Paul, Simon Peter, Sebastian, John the Baptist, and others.