The Tunnel by William H. Gass is a richly allusive novel told by a first person narrator, Professor Kohler, a middle-aged American professor specializing in German history. He has just finished a complete draft of an academic monograph on the topic of Guilt and Innocence in Hitler’s Germany and is struggling to write an introduction to it.
The first reason so many European thinkers appear in this book is that the narrator is a professor of European history and is thinking about the book he is writing on that topic; thus thinkers who provided important sources for his book will be prominent in his thoughts.
Another reason that the work uses so many allusions is that for the sort of educated audience for which Gass is writing, the allusions are a useful shorthand. For example, when thinking about the relative signifigance of a record of the daily trivia of everyday life versus a work of scholarship, Gass invokes Samuel Pepys, a seventeenth-century English writer whose minutely detailed diaries are one of our major sources for everyday life of the period. Henri Frédéric Amiel, a nineteenth-century French thinker, is also known mainly for autobiographical work, and thus is also relevant to Kohler as his struggle with scholarship leads him toward autobiography. André Gide is a French writer who was connected to the existentialist movement, and produced novels, autobiography, and nonfiction, and was not only gay himself but was one of the earliest writers to explicitly defend homosexuality.
Rilke is considered one of the leading poets of Germany, and wrote works wrestling with an intellectual impetus toward atheism balanced against a desire for the spiritual. Kohler's own existential dilemmas echo those found in Rilke's work.