Consider the doubling of the characters. What is the importance of it?

Doubling

Many critics describe Septimus as Clarissa's doppelganger, the alternate persona, the darker, more internal personality compared to Clarissa's very social and singular outlook. Woolf's use of the doppelganger, Septimus, portrays a side to Clarissa's personality that becomes absorbed by fear and broken down by society and a side of society that has failed to survive the War. The doubling portrays the polarity of the self and exposes the positive-negative relationship inherent in humanity. It also illustrates the opposite phases of the idea of life.