Defoe depicts eighteenth-century society as a large markeplace where people struggle to survive. In this struggle, it is difficult to remain moral. Yet, for all his interest in this theme, Defoe came from a Puritan background which urged him to use his works to teach moral lessons. Thus, he approaches Moll's criminal activities and her other immoral actions with a didactic intent. In the Preface, he clearly states that the story of Moll is true and that he has taken all possible care not to give "lewd ideas" through Moll's story. On the contrary, Defoe urges the reader to see the story as an example of repentance. Here the author is torn between his artistry as a narrator who is able to fascinate audiences with Moll's energy and immoral tricks and his Christian beliefs that point to the fact that Moll has to repent in order to be acceptable as a character.
In another passage of the Preface, Defoe returns to Moll's robberies and justifies their detailed descriptions as a warning to his readers against theft and robbers. Here again the Puritan background of the author influences his thoughts as Moll's criminal activities are given an educational relevance for the readers to prevent such behaviors.