One Question

Brothers, a while ago I read in a book by Francois Fenelon, a part that I would like to read again but I don't remember in which book it was. Fenelon compared people's commitment to secular business to the commitment we should make to the gospel. He talks about the gospel as big business, he goes a little on that subject. Does anyone know what book I'm talking about, who can help me with the name of the book?