The Church is necessary for salvation

Since we have no salvation without Christ,
And we do not know Christ without the Church,
It follows that there is no salvation without the Church.

This traditional formula of the Church Fathers (see CCC 846), "Outside the Church there is no salvation", does not mean that Protestants and others are not saved, because this formula is not an answer to the mind's curiosity about the populations of heaven and hell, but an answer to the sincerely seeking heart's question "Where is salvation? Where is the road? What has God done to show me how to be saved?" Similarly, Christ's words to his disciples about "many" choosing the "wide" road to destruction and only "few" finding the "narrow" road to life (Mt 7:14) are not the words of a statistician spoken to a census taker, but the words of a loving heavenly Father to his beloved children, warning them of danger. To the Good Shepherd even one out of a hundred sheep is too many to lose and ninety-nine too few to save (Mt 18:12).

In fact the Church explicitly teaches that many who call themselves non-Catholics are saved. Vatican Council II said that "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" (LG 14), but also that "[t]hose 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 conscience -- those too may achieve eternal salvation" (LG 16) -- not because conscience is an adequate substitute for the Church, but because conscience, too is contact with God.

Catholic Christianity: A Complete Catechism of Catholic Beliefs based on the Catechism of the Catholic Church by Peter Kreeft