Hügel’s selection of Saint Catherine of Genoa as the subject of his biography is made clear when he reveals the importance with which he regards mysticism. Mysticism is an essential element of a developed religion, he says, and the properties of mysticism are best studied in the lives of individual mystics. The traditional lives of mystics are commonly overlaid with legends, and must be subjected to historical criticism. Hügel carefully and critically analyzes the works of earlier writers on the saint as he examines every detail of her life, especially those relating to mystical experiences. He notes that because those who have enjoyed a full mystical experience frequently suffer from mental and nervous illness, care must be taken to distinguish symptoms of illness from spiritual insights.
Hügel especially praises inclusive mysticism, which recognizes the necessity of diverse types of souls and finds in the Kingdom of God the “means of an ever more distinct articulation, within an ever more fruitful interaction, of the various gifts, vocations, and types of souls which constitute its society.” Among inclusive mystics, he notes one of the most prominent to be Saint Catherine of Genoa, which makes her a fitting subject for his study.