Pillar Focus The Apostles Creed: We believe in the Holy Catholic Church
We are the Church that Christ established 2000 years ago (click here). Only through this Church, governed by the Successor of Peter (the Pope) and all bishops who are in communion with him, can one obtain the fullness of the means of salvation (CCC 816). However, we must also recognize that the Spirit of Christ offers much truth and sanctification (something that make us holy) to churches outside our own. This occurs especially in many non-Catholic Christian churches. If a person is properly baptized into a Christian faith (in the name of the Father, Son, and Holy Spirit, use of water, etc.), then he/she is now a part of the the mystical body of Christ. We must therefor consider ourselves brothers and sisters with these Christians (CCC 818).
With regards to other religions outside of Christianity, the Church recognizes that whatever is good or true in them comes from God and is a reflection of his truth. However, we continue to realize that salvation comes from Christ. We understand that if anyone comprehends this truth, and yet refuses to accept or participate in it, there is no salvation for him. This, of course, is not the case for many who are of different religions because it is of no fault of their own that they are not a part of our faith. If they continue to seek God and do his will, he will make eternal salvation available to them just as well. (CCC 846-848).
Something that should be obvious, but serves to complete this post: Even if one is fully incorporated into the one true Church of Christ, who professes the Faith and receives the Sacraments, if he does not persevere in charity (works of love), he will not be saved (CCC 837). We as Catholics posses the "fullness of the means of salvation," but how many of us actually access this "fullness?" We have so many within our own ranks who neither understand the faith, nor pursue understanding it. In the end, they fail to practice Christian necessities. This is not only sad, and does not lead one to salvation, but scandalous.
So with regards to those outside our Church, including even those outside the "Mystical Body," we must take caution to not be so quick to judge. If the members of the Christian church down the road, for example, study their Bibles, pray daily with their families, follow the command of Christ to love God with their "ALL" and to love their neighbors as themselves... well then... they may indeed be experiencing more sanctification then many of us who exist within the normal means of salvation but fail to do these things...
Catechism: THE CHURCH IS ONE, HOLY, CATHOLIC, AND APOSTOLIC
Compendium: (See 161-171)