After his nomination he went to Paris to continue his studies, and then began his lifelong friendship with Arnaud d'Ossat, later cardinal.
In 1573 Barrière, having decided to introduce a reform into his abbey, became a novice there himself, and after obtaining the necessary dispensations, made his solemn profession and was ordained priest, some time after 8 May 1573.
The twelve monks at Les Feuillants, despite the example and exhortations of their abbot, refused to accept the reform, which they disliked so greatly that they tried to poison him.
In 1577 Barrière received the abbatial benediction, re-stated his intention of reforming his monastery, and made the members of the community understand that they had either to accept the reform or leave the abbey; most chose to do the latter and dispersed to various other Cistercian houses, leaving a community of five persons: two professed clerics, two novices, and Barrière himself.
The reform that caused such strong feeling consisted of an ascetic interpretation of the Cistercian rule in its most rigid sense and in many ways exceeded even that.
In 1581 Barrière received from Pope Gregory XIII a brief of commendation and in 1589 one of confirmation, which established the Feuillants as a congregation separate from the Cistercian order, the abbots and general chapters of which mostly opposed it fiercely.
[1] In 1595 Pope Clement VIII exempted the reform from all jurisdiction on the part of Cistercian abbots, and allowed the Feuillants to draw up new constitutions, containing some relaxations of the initial austerities.