Perhaps the comments from the previous pope would help to shed some light on this.
From the book: Crossing the Threshold of Hope, by his Holiness John Paul 2
Under the chapter:
Is only Rome right?
The question is asked:
But the Church? The Catholic Church, in particular? Today many people seem to rebel against the claim that salvation can be found only in the Church. Many Christians-and even some Catholics-ask themselves: Why, among all the Christian Churches, should the Catholic Church alone possess and teach the fullness of the Gospel?
Our Holy Father, JPII responds:
Here, before all else, we need to explain the Christian doctrine of salvation and of the mediation of salvation, which always originates in God. “For there is one God. There is also one mediator between God and the human race, / Christ Jesus, himself human” (1 Tm 2:5). “There is no salvation through any other name” (Acts 4:12).
It is therefore a revealed truth that there is salvation only and exclusively in Christ. The Church, inasmuch as it is the Body of Christ, is simply an instrument of this salvation.
This life, which is life from God and in God, is the actualization of salvation. Man is saved in the Church by being brought into the Mystery of the Divine Trinity, into the mystery of the intimate life of God.
This cannot be understood by looking exclusively at the visible aspect of the Church. The Church is a living body.
Thus, the Council is far from proclaiming any kind of ecclesiocentrism. Its teaching is Christocentric in all of its aspects, and therefore it is profoundly rooted in the Mystery of the Trinity.
Thus, Christ is the true active subject of humanity’s salvation. The Church is as well, inasmuch as it acts on behalf of Christ and in Christ.
men cannot be saved who do not want to enter or remain in the Church, knowing that the Catholic Church was founded by God through Christ as a necessity" (Lumen Gentium 14).
People are saved through the Church, they are saved in the Church, but they always are saved by the grace of Christ. Besides formal membership in the Church, the sphere of salvation can also include other forms of relation to the Church. Paul VI expressed this same teaching in his first encyclical, Ecclesiam Suam, when he spoke of the various circles of the dialogue of salvation (cf. Ecclesiam Suam 101-117), which are the same as those indicated by the Council as the spheres of membership in and of relation to the Church. This is the authentic meaning of the well-known statement “Outside the Church there is no salvation.”
It would be difficult to deny that this doctrine is extremely open. It cannot be accused of an ecclesiological exclusivism. Those who rebel against claims allegedly made by the Catholic Church probably do not have an adequate understanding of this teaching.
Although the Catholic Church knows that it has received the fullness of the means of salvation, it rejoices when other Christian communities join her in preaching the Gospel. This is the proper context for understanding the Council’s teaching that the Church of Christ “subsists” in the Catholic Church (cf. Lumen Gentium 8; Unitatis Redintegratio 4).