Sanskrit sacred literature was born oral. The Vedas were preserved for centuries by prodigious systems of memorisation, and writing entered the tradition late and, at first, uneasily. But once manuscript culture took hold, Devanagari became the script in which the Hindu canon principally circulates: the Vedas and Upanishads, the Bhagavad Gita, the epics and the Puranas, and the vast mantra and tantra literature.
The syllable Om written in Devanagari is now among the most recognised religious marks in the world, standing on temple gateways, title pages and household shrines. In the mantra traditions the letters themselves carry weight: the fifty-odd characters of the alphabet are identified with the petals of the chakras in later yogic texts, and reciting the varnamala, the garland of letters, is itself a devotional exercise.
Jain and Buddhist Sanskrit works also travel in Devanagari, and modern printed editions of Pali and Prakrit texts often use it as well. The script is not itself an object of worship, but it is the ordinary visible body of Hindu scripture, and pious copying of texts in it, especially the Gita, remains a living practice. Household editions of the epics and of popular stotras keep the script in daily devotional use far beyond the temple and the school.