Because, according to the tenets of realism, environment is one of the most important factors in forming character, a detailed description of the character's environment is common. Hugo had all the details he gives us here about convent life from Juliette Drouet; they are all accurate, and for someone interested in convent life, even fascinating. But fifty pages of convent is, for the ordinary reader, far too much.
Hugo does have two practical aims, however, in discussing the convent at length. He wants us to understand thoroughly this atmosphere, which will add its gift of humility to the charity Bishop Myriel taught Jean Valjean and which for so many years will protect Cosette's innocence while not depriving her entirely of feminine mischief such as eating forbidden fruit (the orchard apples and pears) and reading forbidden books (the Rules of St. Benedict.)
He also, in an age when a single church and a Divine Monarchy still vie for French loyalty with an irreligious democracy, wishes to state his position on the religious question. Hugo as a modern man finds convents unnatural and unproductive, but as a poet, he cannot help admiring the sublimity of the monastic sacrifice. And if the convent stultifies, so does pure materialism: there is no Progress without an Ideal. What he himself would prefer is a more active, a more secular form of salvation, the striving for social utopia.
