10 The universality of salvation means that it is granted not only to those who explicitly believe in Christ and have entered the Church. Since salvation is offered to all, it must be made concretely available to all. But it is clear that today, as in the past, many people do not have an opportunity to come to know or accept the gospel revelation or to enter the Church. The social and cultural conditions in which they live do not permit this, and frequently they have been brought up in other religious traditions. For such people salvation in Christ is accessible by virtue of a grace which, while having a mysterious relationship to the Church, does not make them formally part of the Church but enlightens them in a way which is accommodated to their spiritual and material situation. This grace comes from Christ; it is the result of his Sacrifice and is communicated by the Holy Spirit. It enables each person to attain salvation through his or her free cooperation. For this reason the Council, after affirming the centrality of the Paschal Mystery, went on to declare that "this applies not only to Christians but to all people of good will in whose hearts grace is secretly at work. Since Christ died for everyone, and since the ultimate calling of each of us comes from God and is therefore a universal one, we are obliged to hold that the Holy Spirit offers everyone the possibility of sharing in this Paschal Mystery in a manner known to God." "We cannot but speak" (Acts 4:20)
Source: Redemptoris Missio (Vatican.va)