Hazrat Inayat Khan's classic books were among the first to bring Sufism to the West. They remain among the most important introductions Westerners have to the concepts of the ancient religious tradition. In Rassa Shastra, Khan shares his teachings on Sufi ideas about the spiritual and sacred purpose to sex and relationships and stresses "true union," one of the Sufi keys to perfection. He warns against the danger of misusing this most sacred of divine gifts and stresses that misunderstanding sex and sexual desire leads to the deepest problems between men and women.