Barrabas came to us by sea, the child Clara wrote in her delicate calligraphy. She was already in the habit of writing down important matters, and afterward, when she was mute, she also recorded trivialities, never suspecting that fifty years later I would use her notebooks to reclaim the past and overcome terrors of my own.
These are the first words of the novel. They are repeated, almost exactly but in reverse order, as the last words of the novel. The "I" in this quote is Alba, speaking about her grandmother. Although Alba is one of the principal narrators of the story, she almost always uses the third person. This sentence and the epilogue are the only two places she expresses herself in the first person. Clara is Alba's grandmother.
Writing is thematized in The House of the Spirits. This is a metatextual gesture: by having her characters openly discuss writing, Isabel Allende refers to her own process of creating The House of the Spirits. We do not learn until the epilogue that the "I" from these opening lines is Alba. It is easy to assume that the "I" here refers to Isabel Allende herself, since it talks about the process of writing the text we are reading. While Alba is in many ways based on Isabel Allende, it is important to distinguish the two. Allende purposefully created Alba as a character who is both the subject of the novel and one of its narrators.