This question refers to the Monk in "The Canterbury Tales". The fact that the Monk tells story after story, all with the same moral, means that he is a simple man, who perceives the world in absolute and simplistic ways.

The Monk is a part of "The Canterbury Tales," which contains 24 stories by British author Geoffrey Chaucer (1343-1400).
Among the several characters, the Monk tells different stories with the same moral.
All of his stories aim to show characters falling from Grace, that is, going from a high position to a low one.
His purpose, through his tragic stories, is to warn people against trusting wealth and prosperity. Reality can change, and one can go from having everything to having nothing.
The fact that the monk teaches only the same moral reveals that he is a simple man. His view of the world is also simplistic, and he seems to believe in absolute truths.