The four bishops named in the decree were consecrated as bishops on June 30, 1988, by Archbishop Marcel Lefebvre, the founder of the Society of Saint Pius X (SSPX), without the necessary permission from Pope John Paul II. The excommunication was latae sententiae, or automatic, because the action violated canon law.
As the decree from the Congregation for Bishops notes, the removal of the excommunication does not mean that SSPX is now fully reconciled with the Catholic Church: "It is hoped that this step be followed by the prompt accomplishment of full communion with the Church of the entire Fraternity of Saint Pius X, thus testifying true fidelity and true recognition of the Magisterium and of the authority of the Pope with the proof of visible unity."
For their part, SSPX has issued a press release, signed by Bishop Bernard Fellay, expressing "filial gratitude to the Holy Father for this gesture" and looking forward to "talks which will enable the Priestly Society of Saint Pius X to explain the fundamental doctrinal reasons which it believes to be at the origin of the present difficulties of the Church."
Pope Benedict has made the reunion of SSPX with the Church a high priority of his pontificate, not only for its own sake but, as the decree notes, "to be a sign to promote unity in the charity of the universal Church and to try to vanquish the scandal of division." Earlier actions, such as the restoration of the Traditional Latin Mass through the motu proprio Summorum Pontificum, have helped paved the way for the January 21 decree.
Through such prayers as a Devout Exercise for the Unity of the Church, let us all join our prayers to those of the Holy Father, so that Christ's prayer in the Garden of Gethsemane on the evening of Holy Thursday may be fulfilled: "That they all may be one, as thou, Father, in me, and I in thee; that they also may be one in us; that the world may believe that thou hast sent me" (John 17:21).
(Thanks to Rorate Caeli for the translation of the decree and their ongoing coverage of this situation.)