4 ideas
Defoe advertised publicly for eyewitness accounts of the storm, then sorted what came in by reliability. Many scattered first-hand reports, filtered by the witness's accountability, can reconstruct an event no single observer could see whole.
He was there making repairs when the 1703 storm struck, and the tower was swept away with him and everyone in it. Confidence in a structure that has only been tested against ordinary conditions says nothing about how it will survive the extreme case.
After the storm stripped roofs across London, demand for tiles spiked and their price rose several times over. Many householders patched their roofs with boards or thatch or left them open, because they could not afford to repair them properly. A disaster that destroys many assets at once turns ordinary repair materials into scarce goods, so recovery costs rise just as need peaks.
Defoe argues that the storm was not merely a natural event but an act of divine providence. He reads it as a warning and a judgment on England's sins, and he criticizes those who explain it away purely through natural causes. On this view, documenting the damage accurately is also a moral act, because the record is meant to call the nation to repentance rather than just inform it.