Who is Jane from A Severe Mercy and what is their importance?

Jane ia a fellow Oxford student and passionate lover of poetry and literature, Jane is the friend that fills the void of the worship of beauty while Davy is sick the first time and devoted to her Christian study in her waking hours. Jane is a believer, but becomes the personification of the breach of the Shining Barrier for Van as he realizes they were in love with each other during her visit.