Nin's usage of the word incest in this case is metaphorical, not literal. In other words, in this book the word "incest" describes a selfish love where one can appreciate in another only that which is similar to oneself. One is then only loving oneself, shunning all differences. At first, such a self-love can seem ideal because it is without fear and without risk. But eventually it becomes a sterile nightmare. Toward the end of the book, the character called "the modern Christ" puts Nin's use of the word into context: “If only we could all escape from this house of incest, where we only love ourselves in the other."