Prajāpati — the creative function of God, the Creator — fashioned the various disciplines of sādhanā (yajña) according to the needs of different people, together with the wholesome means of enjoying life. It then appointed guardians — the devas, the divine or natural forces — over each such yajña. The yajña is a powerful ritual, outer and inner, by which such guardians are invoked: from the archaic (darśa-pūrṇamāsa, aśvamedha) through the mediaeval (pitṛ, bhūta, manuṣya, ṛṣi and deva offerings) to the modern (homa, pūjā, japa, pārāyaṇa, mantra, dhyāna — and, in a wider sense, perhaps all our technological means as well). Rightly invoked, they are favourable to us. A symbiotic relationship with them is doubly beneficial: it avoids inviting their disfavour, and it helps us obtain what we seek.