If one of you is sad, let her overcome herself so as to recreate with her sister. At the same time, let the one who is cheerful moderate her exuberance so as to accommodate herself to the mood of her sister and, little by little, draw her out of her melancholy. All this should be done for the love of God and to avoid listening to the temptation that might cause you to want to go elsewhere to unburden your soul and to seek satisfaction.
