Pope Boniface VIII proclaimed in the Bull Unam Sanctam in 1302 that "Urged by faith, we are obliged to believe and to maintain that the Church is one, holy, catholic, and also apostolic. We believe in her firmly and we confess with simplicity that outside of her there is neither salvation nor the remission of sins… Furthermore, we declare, we proclaim, we define that it is absolutely necessary to salvation that every human creature be subject to the Roman Pontiff."
One hundred and forty years later, 1442, the Council of Florence proclaimed in its Bull of Union with the Copts that the Church "firmly believes, professes and preaches that all those who are outside the catholic church, not only pagans but also Jews or heretics and schismatics, cannot share in eternal life and will go into the everlasting fire which was prepared for the devil and his angels, unless they are joined to the catholic church before the end of their lives."
Some recent free-thinking theologians have understood these decrees to mean that, as a matter of fact, no one is ultimately saved who is not a member of the Catholic Church at the time of his death. When one examines these decrees in their historic context, this interpretation is highly questionable. The Bull Unam Sanctam affirms that there is no "remission of sins" outside the Church, that is to say, it is not talking only about ultimate salvation, but about sanctifying grace. Examining the decrees prior to the Council of Florence, as well as noting that the Council of Florence's decree draws heavily upon Fulgentius (who held the necessity of being in the Church for grace as well as for salvation), it is probable that the Council of Florence intended to affirm the same: not only the necessity of being in the Church for ultimate salvation, but also for grace. Now, the common teaching at that time was that sanctifying grace can, as a matter of fact, be possessed by those who are, in fact, outside the Church, as in the case of persons baptized in a heretical or schismatic sect, or have not yet come to recognize the error of their sect, and are thus not culpable for their separation from the Church. Consequently, to do justice to these decrees, they have to be understood to mean that God presents man with no other alternative for grace and salvation than incorporation into Christ, in his Church, and yet, in his will for the salvation of all, he in fact saves men who are in invincible ignorance of the necessity of belonging to the Catholic Church for salvation.
To attain, by historical investigation, complete historical certainty regarding the meaning of the decrees may require more inquiry than has been done until now on this matter. However, even granting that the historical data leaves the matter ambiguous, granting that either the superficial interpretation or the context-based interpretation is a possible one, for the Catholic there is another, very important hermeneutic principle: "This dogma [outside the Church there is no salvation] must be understood in that sense in which the Church herself understands it. For, it was not to private judgments that our Savior gave for explanation those things that are contained in the deposit of faith, but to the teaching authority of the Church" (Letter of the Holy Office to the Archbishop of Boston, August 8, 1949).
How does the Church understand this dogma? Pius IX makes three statements that imply interpretations of it or of its consequences:
It must, of course, be held as a matter of faith that outside the apostolic Roman Church no one can be saved, that the Church is the only ark of salvation, and that whoever does not enter it will perish in the flood. On the other hand, it must likewise be held certain that those who are affected by ignorance of the true religion, if it is invincible ignorance, are not subject to any guilt in this matter before the eyes of the Lord. (Allocution Singulari quadam, December 9, 1854)
There is only one true, holy, Catholic church, which is the Apostolic Roman Church. There is only one See founded in Peter by the word of the Lord, outside of which we cannot find either true faith or eternal salvation…. The Church clearly declares that the only hope of salvation for mankind is placed in the Christian faith, which teaches the truth, scatters the darkness of ignorance by the splendor of its light, and works through love. This hope of salvation is placed in the Catholic Church which, in preserving the true worship, is the solid home of this faith and the temple of God. Outside of the Church, nobody can hope for life or salvation unless he is excused through invincible ignorance. (Encyclical Singulari quidem, March 17, 1856)
7. And here, beloved Sons and Venerable Brothers, We should mention again and censure a very grave error in which some Catholics are unhappily engaged, who believe that men living in error, and separated from the true faith and from Catholic unity, can attain eternal life. It is known to Us and to you that they who labor in invincible ignorance of our most holy religion and who, zealously keeping the natural law and its precepts engraved in the hearts of all by God, and being ready to obey God, live an honest and upright life, can, by the operating power of divine light and grace, attain eternal life, since God Who clearly beholds, searches, and knows the minds, souls, thoughts, and habits of all men, because of His great goodness and mercy, will by no means allow anyone to be punished with eternal torment who has not the guilt of deliberate sin.
8. But, the Catholic dogma that no one can be saved outside the Catholic Church is well-known; and also that those who are obstinate toward the authority and definitions of the same Church, and who stubbornly separate themselves from the unity of the Church, and from the Roman Pontiff, the successor of Peter, to whom "the guardianship of the vine has been entrusted by the Savior," cannot obtain eternal salvation. (Encyclical Quanto conficiamur moerore, August 10, 1863)
In the first text the Pope affirms that those who are in invincible ignorance of the fact that the Catholic Church is the Sacrament of Salvation established by God, are not subject to guilt on account of their not entering or not being in the Church. This does not directly imply that these persons can be saved. However, inasmuch as he is clearly making reference to the dogma "Extra Ecclesiam Nulla Salus", it gives a certain indication of how the dogma is to be understood, suggesting that in some sense it doesn't apply to those in invincible ignorance (a complete argument for this implication would, again, involve examining the historical meaning and application of the dogma.)
In the second text the pope, again in the context of the dogma Extra Ecclesiam Nulla Salus, qualifies the impossibility for life (sanctifying grace) or salvation outside the Church to apply to those who are not in invincible ignorance of the necessity of the Church.
In the third text the pope affirms positively that persons in invincible ignorance of the necessity of the Catholic Church for salvation "can be saved", and in recalling the dogma Extra Ecclesiam Nulla Salus, applies it to those who obstinately and stubbornly are separate from the Church.
Pope Pius XII in Mystici Corporis implies a slightly different, though related, interpretation of the dogma: the Church is necessary for salvation, not in such a way that everyone as a matter of fact must belong to the Church to be saved, but in such a way that also those can be saved who belong to the Church only by an implicit desire, inasmuch as they wish to be conformed to the will of God, though without knowing that God's will is for all to enter into the unity of the Catholic Church.
The Holy Office in its Letter to the Archbishop of Boston interprets the dogma in two senses: first as the implication of the command of Christ to be incorporated into the Church by baptism and to adhere to Christ and to his Vicar, so that "no one will be saved who, knowing the Church to have been divinely instituted by Christ, refuses to submit to the Church or withholds obedience to the Roman Pontiff"; secondly, as referring to the fact that the Church is a necessary means of salvation, where the qualification is made that "God, in his infinite mercy, willed that the effects, necessary for one to be saved, of those helps to salvation which are directed toward man’s final end, not by intrinsic necessity, but only by divine institution, can also be obtained in certain circumstances when those helps are used only in desire and longing;" the Council of Trent made this qualification with regard to baptism and penance, and the Holy Office declares that the same thing must be understood of the Church as well: "that one may obtain eternal salvation, it is not always required that he be incorporated into the Church actually as a member, but it is necessary that at least he be united to her by desire and longing." It cites Pius XII and Pius IX as magisterial confirmation of this view.
Vatican II in Lumen Gentium also takes up these two sense of the dogma:
14… Basing itself upon Sacred Scripture and Tradition, it teaches that the Church, now sojourning on earth as an exile, is necessary for salvation. Christ, present to us in His Body, which is the Church, is the one Mediator and the unique way of salvation. In explicit terms He Himself affirmed the necessity of faith and baptism and thereby affirmed also the necessity of the Church, for through baptism as through a door men enter the Church. Whosoever, therefore, knowing that the Catholic Church was made necessary by Christ, would refuse to enter or to remain in it, could not be saved.
15. The Church recognizes that in many ways she is linked with those who, being baptized, are honored with the name of Christian, though they do not profess the faith in its entirety or do not preserve unity of communion with the successor of Peter…. Likewise we can say that in some real way they are joined with us in the Holy Spirit, for to them too He gives His gifts and graces whereby He is operative among them with His sanctifying power.
16. Finally, those who have not yet received the Gospel are related in various ways to the people of God….Those also can attain to salvation who through no fault of their own do not know the Gospel of Christ or His Church, yet sincerely seek God and moved by grace strive by their deeds to do His will as it is known to them through the dictates of conscience. [Vatican II here footnotes the letter of the Holy Office.]
The Catechism of the Catholic Church formally takes up the question of how the doctrine Extra Ecclesiam Nulla Salus is to be understood: "How are we to understand this affirmation, often repeated by the Church Fathers?" (CCC 846) It first states the positive meaning: "Re-formulated positively, it means that all salvation comes from Christ the Head through the Church which is his Body." It cites Lumen Gentium 14 as an explication of this principle and the consequence of it, then rejects an interpretation of this affirmation as referring to those in invincible ignorance: "This affirmation is not aimed at those who, through no fault of their own, do not know Christ and his Church," (CCC 847) and cites Lumen Gentium 16 in explication of how these persons can obtain salvation.
The same doctrine is taught by the Catechism in its section on baptism. An important principle is there articulated, "God has bound salvation to the sacrament of Baptism, but he himself is not bound by his sacraments" (CCC 1257), which is also relevant to the necessity of explicit faith in Christ and membership in the Church:
1260 "Since Christ died for all, and since all men are in fact called to one and the same destiny, which is divine, we must hold that the Holy Spirit offers to all the possibility of being made partakers, in a way known to God, of the Paschal mystery" (GS 22 § 5). Every man who is ignorant of the Gospel of Christ and of his Church, but seeks the truth and does the will of God in accordance with his understanding of it, can be saved. It may be supposed that such persons would have desired Baptism explicitly if they had known its necessity.
The CDF's declaration Dominus Iesus, 2000, also referring to the Letter of the Holy Office to the Archbishop of Boston, explicitly declares that the formula "extra Ecclesiam nullus omnino salvatur" is to be interpreted in the sense that, for those who are not formally and visibly members of the Church, salvation in Christ is accessible by virtue of a grace that comes from Christ, and that has a mysterious relationship to the Church. (Dominus Iesus, n. 20, footnote 82).
The CDF's Doctrinal Note on some Aspects of Evangelization, 2007, implies the same interpretation:
Although non-Christians can be saved through the grace which God bestows in "ways known to him" (Second Vatican Council, Decree Ad gentes, 7; cf. Dogmatic Constitution Lumen gentium, 16; Pastoral Constitution Gaudium et spes, 22), the Church cannot fail to recognize that such persons are lacking a tremendous benefit in this world: to know the true face of God and the friendship of Jesus Christ, God-with-us…. The Kingdom of God is not – as some maintain today – a generic reality above all religious experiences and traditions, to which they tend as a universal and indistinct communion of all those who seek God, but it is, before all else, a person with a name and a face: Jesus of Nazareth, the image of the unseen God. Therefore, every free movement of the human heart towards God and towards his kingdom cannot but by its very nature lead to Christ and be oriented towards entrance into his Church, the efficacious sign of that Kingdom.
The CDF affirms that non-Christians can be saved without (explicitly) "knowing the true face of God and the friendship of Jesus Christ", yet that the grace that is at work in them by its nature leads to Christ and is oriented towards entrance into his Church.