A Simple Path by Mother Teresa (1995)
TL;DR; It is a small part biography of Mother Teresa, and the people at the Missionary of Charity; and part advise and perspective mostly about Prayer, Faith, Love, Service and Peace. The book opens with "The Simple Path": The fruit of silence is Prayer. The fruit of prayer is Faith. The fruit of faith is Love. The fruit of love is Service. The fruit of service is Peace.