The Latin phrase extra Ecclesiam nulla salus means: "outside the Church there is no salvation". The 1997 Catechism of the Catholic Church explained this as "all salvation comes from Christ the Head through the Church which is his Body."
This expression comes from the writings of Saint Cyprian of Carthage, a bishop of the 3rd century. The axiom is often used as shorthand for the doctrine that the Church is necessary for salvation. It is a dogma in the Catholic Church and the Eastern Orthodox churches in reference to their own communions. It is also held by many historic Protestant Churches. However, Protestants, Catholics and the Orthodox each have a unique ecclesiological understanding of what constitutes the Church. The theological basis for this doctrine is founded on the beliefs that (1) Jesus Christ personally established the one Church; and (2) the Church serves as the means by which the graces won by Christ are communicated to believers.
Kallistos Ware, a Greek Orthodox bishop, has expressed this doctrine as follows:
"Extra Ecclesiam nulla salus. All the categorical strength and point of this aphorism lies in its tautology. Outside the Church there is no salvation, because salvation is the Church" (G. Florovsky, "Sobornost: the Catholicity of the Church", in The Church of God, p. 53). Does it therefore follow that anyone who is not visibly within the Church is necessarily damned? Of course not; still less does it follow that everyone who is visibly within the Church is necessarily saved. As Augustine wisely remarked: "How many sheep there are without, how many wolves within!" (Homilies on John, 45, 12) While there is no division between a "visible" and an "invisible Church", yet there may be members of the Church who are not visibly such, but whose membership is known to God alone. If anyone is saved, he must in some sense be a member of the Church; in what sense, we cannot always say.