Help others to prepare for Mass. Discuss its importance.

The Society of Saint Pius X (Latin: Fraternitas Sacerdotalis Sancti Pii X; also known as the SSPX or the FSSPX) is an international priestly fraternity founded in 1970 by the French Roman Catholic Archbishop Marcel Lefebvre. The society is known for rejecting many of the ecclesiastical reforms both influenced or institutionalized by the Second Vatican Council with the claim of maintaining orthodoxy and doctrinal purity among its followers.

The Priestly Fraternity of St. Peter (Latin: Fraternitas Sacerdotalis Sancti Petri; FSSP) is a traditionalist Catholic society of apostolic life for priests and seminarians. The society was founded in 1988 under the leadership of 12 priests who were formerly members of the Society of Saint Pius X.

The Foederatio Internationalis Una Voce or simply Una Voce (Latin for "[With] One Voice"; from the preface to the Roman Canon) is an international federation of Catholic lay organizations attached to the Tridentine Mass.

Richard Nelson Williamson (born 8 March 1940) is an English traditionalist Catholic bishop who opposes the changes in the Catholic Church brought about by the Second Vatican Council. He was originally a member of the Society of Saint Pius X (SSPX), but was expelled from the SSPX in 2012.

Resistance is a group formed by Church Militant and St. Michael’s Media to help Catholics respond to their baptismal call and obligation to increase in personal holiness while at the same time combating the heresies and abuses that have infiltrated the Church.

Sedevacantism is the position, held by a minority of traditionalist Catholics,[1][2] that the present occupant of the Holy See is not truly pope due to the mainstream church's espousal of the heresy of modernism and that, for lack of a valid pope, the see has been vacant since the death of Pope Pius XII in 1958.