In 1599, under the name Baron de Mafflier, by which he was known at court, he renounced the world and entered the Capuchin priory of Orléans. He embraced the religious life with great ardour, and became a notable preacher and reformer. In 1606 he helped Antoinette d'Orléans, a nun of Fontevrault, found the reformed order of the Filles du Calvaire, and he wrote a manual of devotion for the nuns.