India's classical religious literature spans an unusually long and layered textual tradition, beginning with the Rigveda and the other three Vedas, composed in Vedic Sanskrit and transmitted for centuries through exact oral memorization before being fixed in writing, a preservation method so rigorous that reciters could reconstruct a text precisely even where transmission drifted elsewhere in a lineage.
The Upanishads, composed later and appended to the Vedic corpus, shifted the tradition's center of gravity toward philosophical inquiry into the nature of self and reality, supplying much of the vocabulary later Hindu philosophical schools would debate for two thousand years. The two great epics, the Mahabharata and the Ramayana, developed over centuries through oral and later written transmission and carry embedded religious teaching within their narrative frame, most famously the Bhagavad Gita, a philosophical dialogue set within the Mahabharata that has become one of Hinduism's most widely read texts in its own right.
The Puranas, composed later still, organized much Hindu mythology, cosmology, and sectarian devotional material, including the narratives feeding Vaishnava and Shaiva traditions, into the forms in which they are known today. Buddhism and Jainism, both native to India, produced parallel textual traditions of comparable depth, the former largely in Pali and Sanskrit and the latter chiefly in Ardhamagadhi Prakrit, meaning India's classical output spans several distinct religious systems rather than one continuous line. Sikhism's Guru Granth Sahib, compiled far later in Punjabi and other regional languages, extended this textual tradition into the early modern period.