The bubonic plague was a punishment from God

At the time, the Black Death was widely believed to be a punishment from God, sent as people became more and more sinful over time. People even tried to rid themselves of the disease by practicing severe self-flagellation to repent.^[1] ` A preacher in the 14th century reported to the Pope that a “strange image in the sky was the prelude of the outbreak of the plague. One hour at noon later on March 20th, 1345, the time when the three stars meet at Aquarius, will be the symbol of death."^[1] Many people who caught the disease reported hallucinating the devil and ghosts. This also led to the massacre of perceived 'heretics'.^[2] This is indicative of the lack of understanding about spreadable diseases in general. As opposed to taking precautionary measures, believing the Black Plague was sent from God would have helped its spread, not only because it encourages an attitude based on the idea that getting the disease is pre-determined. This attitude also encouraged gatherings, spurring on the spread of disease. For instance, the self-flagellation happened in groups in town squares.^[2]

[P1] The bubonic plague was seen as being sent from God. [P2] This made the pandemic much more deadly.