In the early centuries of the first millennium BCE, a remarkable breakthrough occurred within India's ancient spiritual civilization. The Vedas had been "heard" (śruti) by the Hindu seers (ṛṣiḥ) sometime before this watershed moment; they are "apauruṣeya," not of human origin. 

The Vedas evolved from the original form of uninterrupted sacred verse (saṁhita) and their embodiment within holy rituals (brāhmaṇam) into the forest ashrams of yogic mystery schools, where they were internalized through mantras, meditation, and yogic practices during the āraṇyaka phase.

The Upanishads gather this sacred wisdom in forest texts that embody the early experiences of spiritual enlightenment, which shine in humans. Every Upanishad begins with a Shanti mantra, a peace prayer that prepares the body, mind, and heart for knowledge that transcends this world.