This much is clear: If someone comes to know that the Church is necessary for salvation and does not become a Catholic, he or she cannot be saved.
But what does it mean for someone to “know that the Church is necessary for salvation”? The documents of the Church always say: If someone knows this but does not act upon it, he cannot be saved. Are there really such people? It might seem as if those who are interested in their own salvation—e.g., practicing Anglicans, Orthodox, Lutherans—have what they believe are “good reasons” not to convert; and it seems that those who do become convinced that the Catholic Church was founded by Christ are precisely the ones who convert—unless some accident intervenes, like a car crash on the way to RCIA.
There might be some rare exceptions. Simone Weil was a strange person, a Jewess who fully believed in Christ and in the Catholic Church but did not convert because she believed that a Jew betrays the Jewish people by converting. But it seems abnormal to see that “X is necessary for Y,” and then not to do X if one desires Y. It would be like saying: “God really wants me to go to the Island; I can get to the Island only by ship; therefore… I won’t take the ship.” Say what?
It would be hard to claim (as does much of modern theology) that people who care little or nothing about the salvation of their immortal souls are acting on the basis of an implicit desire for salvation. But those who want to be saved from sin and inherit eternal life do seem to have an implicit desire for Christ and His Church. The problem is this. If one takes Church statements from the past half-century at face value, it’s hard to see how any “sincere person” could be excluded from the Kingdom of Heaven.
Now, we are not looking for ways to exclude anyone—the more who are saved, the greater God’s glorification!—but we do not want to empty the Cross of Christ of its power and the Church of her divine mission. Extra ecclesiam nulla salus (“outside the Church there is no salvation”) should not be reduced to pure vacuity, dissolved into a pious platitude such as: “Everyone is saved who does God’s will to the extent that he understands it.” That would make of the Incarnation and Passion, not to say the witness of martyrs and missionaries, a ridiculous miscalculation and a tasteless overacting.
Another way of posing the question: What does it mean for someone to be “in good faith” or “in bad faith”? Still another way of posing the question: How vague or specific must the “implicit desire” be in order to function as a desire for salvation? Is it enough to desire generally to be a happy, peaceful, just person? Does one have to believe (as the Epistle to the Hebrews says) that there is a God who rewards the good and punishes the evil? St. Thomas seems to say different things in different places about how much explicit faith is necessary.
Let’s make a comparison. To say that “the Church is necessary for salvation” is much like saying that “the use of a Saturn V is necessary in order to get to the moon.” One cannot get to the moon in a boat, a plane, or by means of a ladder, and in the same way, one cannot get to heaven by means of a false religion. The question about knowledge comes up because God is interested in saving men, while he is not especially interested in getting them to the moon. If God wanted to get men to the moon, then it might have been the case that “if one knows that a Saturn V is necessary to get to the moon, and refuses to use one, then one cannot get to the moon.”
One might, nevertheless, end up on the moon anyway, if one believed that one can get to the moon by means of a ladder—if one’s belief was held with invincible ignorance. When we say that a Saturn V is necessary to get to the moon, we are referring to the means available to men; we are not referring to the power of God, which is capable of getting men to the moon without a Saturn V. And in the same way, God can save men without visible membership in the Church, even though in such a case, the means on the part of the man is essentially inadequate, just as a ladder is inadequate to get to the moon.
It must be rather uncommon that a man has explicit knowledge that the Church is necessary for salvation but refuses to enter. However—and this is far more common—one cannot be saved if one is proximately able to know that the Church is necessary for salvation, but is culpably ignorant of this fact.
If, therefore, someone is saved who is not joined to the Church by the ordinary means, we should say he is joined by “extraordinary” means. If one can be saved only by being in a state of grace, and if that grace is given in and through the Church, then all who are saved must belong to the Church.
The distinction we need is the distinction between being joined to the Church simply speaking, and being joined to the Church in a certain respect. All who are saved are joined to the Church in a certain respect, insofar as one cannot be saved without being in the state of grace, which is a bond of unity with the Holy Spirit and thus with the Church. But not all who are saved are joined to the Church simply speaking, since only those in full union with the Church in the external forum belong to the Church simply speaking. The latter is the teaching of Mystici Corporis and Mortalium Animos. (The Feeneyites claim not only that this constitutes membership in the Church simply speaking—a point on which they are quite correct—but also that none are saved without membership in the Church simply speaking.)
It is indeed absolutely necessary for salvation to be joined to the Church in some respect, just as it is necessary to be in the state of grace. Because “membership in the Church” is truly necessary, and yet the popes speak of the possibility of salvation for invincibly ignorant souls who are not members simply speaking, many (such as Fr. William Most) take the dogma extra ecclesiam nulla salus to signify the necessity of membership in some respect.
Taken as the primary meaning of the dogma, however, that intrepretation must be incorrect. For precisely because the Church is necessary for salvation, one cannot be saved who knows—or is proximately able to know—that the Church is necessary yet who refuses to join in the external forum, and dies thus separated. If the necessity of the Church for salvation was no more than the necessity of the state of grace, then this conclusion would not follow. A Protestant might have been baptized as a child, thereby attaining the state of grace (for sanctifying grace is communicated through baptism); he might know that union with the Catholic Church is necessary, but (on the false hypothesis under discussion) only to this degree: that he persevere in the state of grace. He could not be lost for refusing to join the Church externally, because no reason will have been given why he is under the obligation of so joining.
In other words, when the necessity of the Church for salvation is understood correctly as “the necessity of full communion with the visible, hierarchical Church founded by Christ,” then any person who becomes aware of this demand—implicit in the very foundations of the Christian faith—must become a Catholic in the external forum in order to be saved. In contrast, if the necessity were understood vaguely as the necessity of “being in a state of grace” or “being moved by the Holy Spirit,” there could never be a binding reason for any non-Catholic to become Catholic; all reasons would be merely provisional and personal (such as, “I do not think I can persevere in a state of grace without the sacraments the Church offers”). This, unfortunately, is exactly what ecumenists tend to say today, if indeed they do not go further and positively discourage conversion.
We are now finally in a position to tie these threads together. As explained by the Holy Office in 1949, the dogma extra ecclesiam nulla salus signifies the necessity of belonging to the Church simply speaking—yet precisely as a necessity of means, not as an intrinsically necessary component equivalent to sanctifying grace. (The reason, in brief, is that it would be metaphysically impossible for a soul to enter heaven without being sanctified, but it is not metaphysically impossible for God to sanctify someone who is not a member of the Church simply speaking.) Hence, it follows that one who knows the necessity of the Church cannot be saved if he refuses to join externally. So the Feeneyites are correct in saying that the necessity of membership in the Church is a necessity of membership simply speaking, but they are incorrect in believing that from this necessity it follows as a question of fact that no one is saved who is not a member of the Church simply speaking.
Membership in the Catholic Church is necessary simply speaking as a necessity of means (the sacramental life of the Church, acceptance of her doctrine and discipline, etc.); there is no other way given to man whereby he may attain his salvation. Explanation: In giving grace, God is not bound to the sacraments He has instituted, nor, more generally, is He bound to any created means. Therefore, it is within God’s power that a man could be saved apart from full communion with the Catholic Church, but it is not within man’s power to win salvation apart from that communion. The only path to salvation accessible to man is the one Christ has revealed and established for our benefit and for God’s honor. This is why it would be contrary to God’s will, and sinful, not to follow this path to the extent that one knows it or can proximately know it.
Membership in the Catholic Church is necessary in some respect as a necessity of end (union with God through grace), without which no man can be saved at all, even by divine power. In other words, anyone who is saved will have been living by charity and will have been led by God’s good spirit into the promised land. There is no way to be saved apart from the grace of the Holy Spirit, which is the inner core, the “soul,” of membership in the Church. This grace is always the gratia Christi, always related to the Passion, and therefore always objectively related to the Church which is Christ’s Mystical Body, the “place” where one is united to God. It is thus also objectively tied to the Most Blessed Sacrament, since “unless you eat My flesh and drink My blood, you shall not have life within you” (Jn 6:53).
Even though nothing supernatural is within man’s power (hence we cannot ever truthfully say “a man saves himself”), God has given a means whereby man can “work out his salvation.” By exercising his free will with the help of the actual graces God never denies, a man can take all necessary steps in order to be saved—he can seek and receive baptism and instruction, adhere to the Creed, pray as the Church instructs him to pray, frequent the sacraments. All those things require the assistance of grace, and yet have been designed by God in such a way that a man can cooperate with grace simply by willing to do so. For example, I can always will to go to Mass on Sunday, and if no one stops me, I can actually go; I am never, as it were, unfree with respect to such a good. God in His great mercy has made it this way in order to render salvation something attainable for all who desire it.
(This article has been updated.)
 There are certain things impossible for man, simply speaking. There is nothing a man can do to save himself apart from the one true religion God has instituted through His Son. To be saved apart from it would involve a contradiction in terms. Still, this does not mean that God, in His mercy, cannot save a man who is factually distant from that religion, although not personally and obstinately opposed to it. Here, the possibility is entirely on God’s side, and not on man’s. “What is impossible for man is possible with God” (Lk 18:27).
 Ludwig Ott’s discussion of votum implicitum agrees with this position: “The necessity for belonging to the Church is not merely a necessity of precept, but also a necessity of means, as the comparison [of the Church] with the Ark, the means of salvation from the biblical flood, plainly shows. The necessity of means is, however, not an absolute necessity, but a hypothetical one. In special circumstances, namely, in the case of invincible ignorance or of incapability, actual membership of the Church can be replaced by the desire (votum) for the same. This need not be expressly present, but can also be included in the moral readiness faithfully to fulfill the will of God (votum implicitum). In this manner also those who are in fact outside the Catholic Church can achieve salvation.” Fundamentals of Catholic Dogma, ed. James Bastible, trans. Patrick Lynch (Rockford, Il.: TAN Books and Publishers, 1974), p. 312.