The SSPX's Third Order exists for the sanctification of the laity by uniting them in a special manner to the family of the priestly society and the graces obtained through its apostolic work.
What is the Third Order?
"Third Order" signifies membership of the laity in a religious order. The laity has always been distinguished from clergy or religious. A third order gives the laity a degree of participation in what is proper to the clergy or religious.
The Importance of the Third Order Today
Letter from Fr. Pagliarani on the Third Order of the Society of Saint Pius X
The Spirit of the SSPX by Archbishop Lefebvre
A compilation of five articles written by Archbishop Lefebvre in which he outlines to the SSPX's members the spirit of their priestly society.
What are the Origins of a Lay Third Order in the Church?
If a definition were to be given—a third order is an association of laity who are members in a religious order. It is in this light that Tertiaries are part of the family and truly members of any religious order.