In the sixth year the lawyer devours over six hundred volumes of language, philosophy and history. Why do you think he is so motivated?

He is motivated because he really wants to understand humankind and all forms of genius from different parts of the world.

Explanation:

In the sixth year, the lawyer now wants to know more about the world, about humankind and all forms of genius that existed in all parts of the world. For this reason, he begins to read philosophy and history. From these, he was able to understand how humans thinks and live, and the reasons behind these. He was no longer reading for just entertainment as in the first year and second year of his sentence when he had no interest in learning anything about the world. This phase (the sixth year) of his prison sentence provided him with a desire to better understand the world and the people living in it.