"There is, I should say, a very serious error involved in a Christian parent's committing the training of his children to unconverted persons, or even to those whose hearts are not one with him as to separation from the world. It is natural that a child should look up to, and follow the example of, one who has the training and management of him. Now, what can a teacher make of a child, save what he is himself? Whither can he lead him but to where he is himself? What principles can he instill save those which govern his own mind, and form the basis of his own character? Well, if I see a man governed by worldly principles — if I see plainly, from his whole course and character, that he is an unconverted persons shall I commit to him the training or instruction of my children, or the formation of their characters? It would be the height of folly and inconsistency so to do. As well might a man who desired to make an oval-shaped bullet cast the melted lead into a circular mould. The same principle applies to the reading of books. A book is decidedly a silent teacher and former of the mind and character; and if I am called to look well to the character and principles of the living teacher, I am equally so to look to those of a silent teacher. I am quite convinced that, in reference both to books and teachers, we need to have our consciences stirred and instructed."

From Thou and Thy House or The Christian at Home by C. H. Mackintosh