In one of the play’s many instances of sharp social satire, Peachum comments on the irony of the relationship between criminals and the legal profession:
A Lawyer is an honest Employment, so is mine. Like me too he acts in a double Capacity, both against Rogues and for ’em; for ’tis but fitting that we should protect and encourage Cheats, since we live by them.
When Filch claims that he is considering “going to sea” or working on a ship to avoid the dangers of the criminal lifestyle, Mrs. Peachum ironically commands him to learn the Bible so that he can commit crime without fear of repercussion:
Unlock with LitCharts A+Poor Lad! how little does he know as yet of the Old-Baily! For the first Fact I’ll insure thee from being hang’d; and going to Sea, Filch, will come time enough upon a Sentence of Transportation. But now, since you have nothing better to do, ev’n go to your Book, and learn your Catechism; for really a Man makes but an ill Figure in the Ordinary’s Paper, who cannot give a satisfactory Answer to his Questions.