The Church does indeed teach this, Bergon.
Show me what your referring to in Church teaching.
In the third century some Christian groups wanted to be outside the Church. St Cyprian, one of the Fathers of the Church, said a Christian cannot be saved without the Church.
The Second Vatican Council in
Lumen Gentium 14: “Whosoever, therefore,
knowing that the Catholic Church was made necessary by Christ, would refuse to enter or to remain in it, could not be saved”. (Emphasis mine)
The Church’s teaching is: one who is aware of the presence of revelation is obliged by his conscience to belong publicly and, not only in his conscience, in his heart, to this Catholic Church by remaining in communion with the Pope and those bishops in communion with him.
The Church also teaches: if one is inculpably ignorant of this truth they are not necessarily condemned for that reason. We must hope that those who do not belong to the Church through no fault of their own, but who follow the dictates of their God-given conscience, will be saved by Jesus Christ whom they do not yet know.
However, if a Catholic says today: “I am going to put myself outside the Church,” we would have to respond that without the Church, that person is in danger of losing salvation.
There is no salvation outside the Church if you’re aware of revelation and choose to reject the Church. If one has no knowledge of Christ and revelation being outside the Church doesn’t deny you salvation.
Consequently, it is not an absolute Church teaching that there is no salvation outside the Catholic Church.