One of the most interesting developments in post-conciliar theology has been Karl Rahner’s idea of “anonymous Christians.” He taught that God offers his grace to everyone and reveals himself in the interior offer of grace. Grace, moreover, is always mediated through Christ and tends to bring its recipients into union with him. Those who accept and live by the grace offered to them, even though they have never heard of Christ and the gospel, may be called anonymous Christians.Here's my analogy. Imagine that salvation is eating dinner. You sit down at the table, request the steak, which is promptly passed, pull our your knife and fork, and slice away (my apologies to vegetarians out there, but I like eating meat).
Although Rahner denied that his theory undermined the importance of missionary activity, it was widely understood as depriving missions of their salvific importance. Some readers of his works understood him as teaching that the unevangelized could possess the whole of Christianity except the name. Saving faith, thus understood, would be a subjective attitude without any specifiable content. In that case, the message of the gospel would have little to do with salvation.
Imagine that a thick fog fills the room so that you cannot see anything. You walk in, tripping over someone else's foot, bumbling to find something to eat (poking yourself and many others in the eye), ending up with a plate of something that's as likely to be the plant from the middle of the table as it is to be food.
Some people would be horror stricken if it were thought that any true Christian could possibly entertain the notion that unevangelized people (those who haven't heard) could be "saved". After all, wouldn't such a theology destroy any need for missions?
Now think of my foggy dinner analogy. There might be one man who walks in, comfortably sits down to a plate of food, happens to pick up the right instruments, and proceeds to enjoy a wonderfully tasty (though probably not peaceful, with all those bumblers around him) meal. Why does he need evangelizing? Now imagine that the fog is cleared away and he sees clearly for the first time. Who's going to claim that that act is useless?
This isn't to say that I agree with Rahner's conclusions or theology in the least. What I am saying is that even if Rahner's wrong, it's not because his theology opposes missions.
Knowing the truth doesn't mean you're gonna act appropriately. Two men emerge from the fog and see the table. One man sees a knife and plunges it into his steak. Another man sees the knife and plunges it into his wife. Both men saw clearly and yet only one man understood.