“Since man always remains free and since his freedom is always fragile, the kingdom of good will never be definitively established in this world. Anyone who promises the better world that is guaranteed to last forever is making a false promise; he is overlooking human freedom. Freedom must be constantly won over for the cause of good. Free assent to the good never exists simply by itself. If there were structures which could irrevocably guarantee a determined and good state of the world, man's freedom would be denied, and hence they would not be good structures at all.”