Charles Sylvester in Journeys Through Bookland (volume 1, although this section was later moved to a different volume called ‘Guide to Journeys Through Bookland):
“… think for a moment on the permanent value of all that is read. The mind holds things in abeyance, brings them out to the light now and then, and each time finds them more and more intelligible and influential. Many a maxim learned in youth when an understanding of it was impossible becomes a power for good for the person in later years, when its inner significance appears.”
“Moral instruction is difficult. A thousand little things tend to neutralize it, and there is an almost universal spirit of opposition to moral teaching on the part of youth.”
An indirect way is best, he then explains, and this is easily achieved through the best books.