The Upanisads' is the Hindu equivalent of the Christian New Testament. It is a collection of spiritual treatises written in Sanskrit between 800 and 400 BCE. Typically an Upanisad recounts one or more sessions of teaching, often setting each within the story of how it came to be taught. These thirteen texts, the principal Upanisads, are devoted to understanding the inner meaning of the religion: they explicate its crucial doctrines - rebirth, the law of karma, the means of conquering death, and of achieving detachment, equilibrium and spiritual bliss. They emphasise the perennial search for true knowledge.