Complex sentence: The sight drafts he receives from his grandfather are the only link to his home, he doesn't pay much attention to his grandfather's letters, the only one mentioned in the whole book is handled in two short lines among many others.
Split into simpler sentences: The sight drafts he receives from his grandfather are the only link to his home. He does not pay much attention to his grandfather's letters, the only one mentioned in the whole book is handled in two short lines among many others.