Lumen Gentium does indeed state that non-Catholic Christians can not be saved, but there are some important qualifications. First of all, part of the statement in Chapter II, Section 14 states:
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.
This is important, because the section only affects Christians who "
knowing that the Catholic Church was made necessary by Christ" refuse to become Catholics. It can be said that anyone who holds this belief would, of course, become a Catholic and that anyone who does not become a Catholic does not hold that belief. Protestants and others are off the hook.
Second, Lumen Gentium must be read in the context of Dignitatis Humanae, also issued by the Second Vatican Council. This states:
- This Vatican Council declares that the human person has a right to religious freedom. This freedom means that all men are to be immune from coercion on the part of individuals or of social groups and of any human power, in such wise that no one is to be forced to act in a manner contrary to his own beliefs, whether privately or publicly, whether alone or in association with others, within due limits.
The council further declares that the right to religious freedom has its foundation in the very dignity of the human person as this dignity is known through the revealed word of God and by reason itself.
In Dignitatis Humanae, section 2 grants non-Catholics the absolute right, under Catholic teaching, to religious freedom. But is the exercise of that freedom to be considered as being at the expense of their salvation? For this I turn to section 1:
First, the council professes its belief that God Himself has made known to mankind the way in which men are to serve Him, and thus be saved in Christ and come to blessedness. We believe that this one true religion subsists in the Catholic and Apostolic Church, to which the Lord Jesus committed the duty of spreading it abroad among all men ...
This Vatican Council likewise professes its belief that it is upon the human conscience that these obligations fall and exert their binding force. The truth cannot impose itself except by virtue of its own truth, as it makes its entrance into the mind at once quietly and with power.
Religious freedom, in turn, which men demand as necessary to fulfill their duty to worship God, has to do with immunity from coercion in civil society. Therefore it leaves untouched traditional Catholic doctrine on the moral duty of men and societies toward the true religion and toward the one Church of Christ.
I notice that the bishops say three times in the space of the above extract that what follows is their "belief" - thus not immutable truth. The council only requires non-Catholics to follow their consciences, not necessarily bound by the teachings of the Church, saying "The truth cannot impose itself except by virtue of its own truth."
So, yes, Lumen Gentium does say that non-Catholic Christians can not be saved, but only if they actually know the requirement to become Catholics. In Dignitatis Humanae, they are to follow their own consciences in reaching the truth as to whether they should be Catholics.