Dickens's rather rhetorical chapter on the decadent Monseigneur who has been waited upon for so many centuries that he can no longer swallow his morning chocolate without the aid of four strong men exemplifies the state of the French aristocracy. While the Monseigneur--who represents all the aristocracy--has felt that the world is made for his pleasure, he finds that certain "vulgar embarrassments crept into his affairs, both private and public." The Monseigneur has allied himself with a Farmer-General since he is now becoming poor.
The Farmer-General is a tax collector--"the greatest reality among the personages who attended at the hotel of Monseigneur"-- and, since he has become poor, the Monseigneur pulls his sister from a convent and has her marry this tax collector in order to preserve the family estate and his prestige in court.
We don't really know the specific benefit the Monseigneur gets from this rather callous move, but that doesn't really matter. What we do know is that he was willing to do such a thing and his sister had no choice in the matter. This is the world of the aristocracy at the time. Every alliance and every action was designed to add either power and position or wealth to the family and its holdings.
The great irony is that, while poor and suffering, the common people got to marry for love. They may not have had much else, but they did have a freedom not allowed the most "free" in the world of the French Revolution. A Tale of Two Cities clearly portrays this attitude in both London and Paris throughout the novel.
In Book II Ch.7 "Monseigneur in Town" Dickens bitterly satirizes the decadent French aristocracy through the portrayal of the dissolute French nobleman, the Monseigneur. Twice a month in a hotel in Paris he displays his luridly pompous life style to his followers. The Monseigneur who needs four elegantly liveried servants to help him drink his cup of chocolate is completely oblivious not only to the grim socio-economic conditions of his age but also to the precarious condition of his personal financial position. He has been living far beyond his means and is always in arrears of tax to the French King.
In order to stave off the danger of being arrested by the authorities he pleases the tax collector the "Farmer-General" by marrying off his sister to the avaricious "Farmer-General." Dickens underscores the fact that the French aristocracy was so corrupt that they would go to any extent - even sacrifice the virtue of their own sister - to maintain their own vulgar pompous life style:
"The earth and the fulness thereof are mine, saith Monseigneur."