Having decided to take Uchiha Sasuke as his disciple, Uchiha Toukan naturally intended to teach him properly.
Choosing Confucian classics as Sasuke's introductory reading was also the result of careful consideration on Uchiha Toukan's part. First of all, Sasuke was not even seven years old yet, and considering his older brother's past tendency to overthink all sorts of strange things from a young age, it was particularly important to first establish a relatively simple moral framework. This would let the child know which traits were good and which were undesirable—in other words, to first establish a sense of outward dignity and propriety.
Once Sasuke discovered that this set of concepts was no longer sufficient to explain the world before his eyes, he would naturally fall into confusion. Only at that point would he be taught the real substance, filling the outward shell with true inner meaning.
Chapter 42