When one faces someone else or some situation that is working or fighting against one goal

a foil character shows contrast with the qualities of another character. to emphasize the traits of the other character is the main objective. cassius is a foil to brutus, and brutus is a foil to antony. both cassius and antony conspire to kill caesar, but cassius is more prone to treachery than brutus is. thus, easily gives in to his evil ambition. brutus is a foil to antony because brutus’s honesty and simplicity are in clear contrast to antony’s qualities of deception and over-ambition.

answer :

the best summary of this reading passage from "a tale of two cities" by charles dickens is "yet, monseigneur had slowly found that vulgar embarrassments crept into his affairs, both private and public; and he had, as to both classes of affairs, allied himself perforce with a farmer-general." it describes that state of private and public affairs of the monseigneur perfectly.