At the desire of Cardinal Richelieu he began a controversy with the Benedictines, denying Jean Gerson's authorship of "De Imitatione Christi". Richelieu intended to make Naudé his librarian, and on his death Naudé accepted a similar offer from Cardinal Mazarin. For the next ten years he devoted himself to bringing together from all parts of Europe the assemblage of books known as the "Bibliothèque Mazarine". Mazarin had brought with him to Paris a collection numbering over 5,000 volumes. Like Naudé, he believed in an open library to be used by the public for the public good. In 1642 he purchased a building to house his library and he instructed Naudé to build up the finest collection possible.