Hymns to Agni from the Rig Veda

 “The preoccupation of the Mystics was with self-knowledge and a profounder world-knowledge; they found out that in man there was a deeper self and inner being behind the surface of the outward physical man, which it was his highest business to discover and know. “Know thyself” was their great precept, just as in India to know the Self, the Atman became the great spiritual need, the highest thing for the human being”