C. S. Lewis, from “On the Transmission of Christianity”:

None can give to another what he does not possess himself. No generation can bequeath to its successor what it has not got. You may frame the syllabus as you please. But when you have planned and reported ad nauseam, if we are sceptical we shall teach only scepticism to our pupils, if fools only folly, if vulgar only vulgarity, if saints sanctity, if heroes heroism. Education is only the most fully conscious of the channels whereby each generation influences the next. It is not a closed system. Nothing which was not in the teachers can flow from them into the pupils. We shall all admit that a man who knows no Greek himself cannot teach Greek to his form: but it is equally certain that a man whose mind was formed in a period of cynicism and disillusion, cannot teach hope or fortitude.