The brothers’ ability to overcome difficulties to succeed as scholars.
Explanation:
The excerpt begins by informing us of the difficult personal problems and the meager financial support that the brothers faced from 1805 to 1812. It also highlights that, despite these problems, the brothers could prove themselves as innovative scholars in German philology. Therefore, that the author introduces is the brothers’ ability to overcome difficulties to succeed as scholars.
Tom asks Huck to take a shirt from the clothesline which Jim can use as a journal while he is in prison. Huck is surprised, because Jim can't even write.
