The Catholic religion was the only one permitted in France following the 1685 Revocation of the Edict of Nantes. This royal decision obliged all persons wishing to assume an official position to first prove their Catholicity. A certificate of Catholicity could also be useful in ensuring a Christian burial for those who died far from home.

The Certificate of Catholicity
Certificate of Catholicity issued to Sieur Michel Leneuf de La Vallière, captain in Port-Toulouse, October 13, 1730
FR CAOM COL C11B 11 fol. 217