Having embraced the ecclesiastical state, he became one of the secretaries of the archbishop of Rouen and took advantage of the leisure left to him by this modest employment to become familiar with reading charts and study in depth the History of Normandy.
Provided the cure of Saint-Jacques-sur-Darnétal, he soon resigned this benefit and accepted instead a position of librarian of the metropolitan chapter, which would facilitate the means to indulge his taste for historical and literary research.
In the trial the chapter had to support against the Benedictines of the abbaye de Saint-Ouen, father Saas showed great zeal for the maintenance of the privileges of his church, and he was rewarded in 1751 by a canonry.
The assiduous reading of historical dictionaries proved him that those who were most esteemed were not error-free, and he was quick to point out, in small scholarly writings, those he had noticed.
It passed into the hands of Drouet, who intended to make use of for a supplement (Éloge de Saas, by Cotton, p. 30).