http://www.usccb.org/catechism/text/pt1sect2chpt3art9p3.htm
The church is both spiritual and physical - the invisible mystical Body and Bride of Christ (referred to as the
church)and the visible community of all believers (referred to as the
Church). The church has both a visible hierarchy and an invisible hierarchy, having those appointed to teach and others appointed to be taught (1 Corinthians 12).
If someone
knows that Christ founded His church with a visible teaching authority vested in the hierarchy of the Church, and rejects that authority anyway, then he cannot be saved because in rejecting the Church the person is intentionally rejecting that which he knows Christ founded. "Hence they could not be saved who, knowing that the Catholic Church was founded as necessary by God through Christ, would refuse either to enter it or to remain in it." (CCC, p 846).
But there are many true Christians who sincerely, but mistakenly, believe that the Catholic Church is apostate and that it is not a legitimate part of Christs Bride, the church. These people are not rejecting the true Catholic Church, they are rejecting a qrotesque distortion of it.
Nonetheless, through Baptism these Christians are a part of the church (the mystical Bride), and through the unity of Christ are thus related to the Church (the visible instirution). The Church teaches that "Those who, through no fault of their own, do not know the Gospel of Christ or his Church, but who nevertheless seek God with a sincere heart, and, moved by grace, try in their actions to do his will as they know it through the dictates of their consciencethose too may achieve eternal salvation" (CCC, p 847)
Its important to remember that many of the statements of the past were made to address the issue of those who
knew that the Church is the legitimate institution of the church and rejected it anyway. The issue of those who
dont know it is different, and the Churchs statements about that clearly say that people who are not visible members of the Catholic Church can nonetheless be saved. If they are, its all by the grace of Christ.
One cannot truly reject what one does not first truly know.