Rigveda is the oldest of all the Vedas. The ancient Rishis (sages), who created the Vedas, have treated the forces of nature as Devata(God) since the natural forces have been created by Brahm–the Almighty. The Rigveda contains hymns devoted to every natural force like the rivers, streams, mountains, Vayu (the wind God), Rudra (God of storm) and Indra.
After Rigveda came the Yajurveda. It is devoted to Karmakanda (the karmic path) and was followed by Mimamsa (treatise on Karmakanda). After Yajurveda, when society witnessed creative pursuits and the flowering of dance, drama and music, we have all this contained in the Samveda. It shows how to sing the vedic hymns so minutely specified through the gyan shastra. The focus is also on smritishastra—the art of memorizing the Vedas. The last of the Vedas, Atharvaveda is a treatise on specialized subjects like architecture, engineering, archery and ayurveda.
The Vedas contain infinite knowledge. People over successive generations became the followers of one or the other Veda. Thus we have the Rigvedis or the Yajurvedis. Then there are also Dwivedis and Chaturvedis, who followed either two or all the four Vedas. People also started picking single streams or just one part of the Vedas like the ĀPASTAMBA Sutras and started mastering them. The Dharmasutra of Āpastamba forms a part of the larger Kalpasūtra of Āpastamba. It contains thirty praśnas, which literally means ‘questions’ or books.
In ancient times, nothing was in writing. Knowledge was memorized and passed on from the Guru (teacher) to the Shishya (pupil) in the Gurukul through the typical “Guru-Shishya Parampara”.
The discussions covering the Vedas that took place in the Gurukul followed the question answer pattern with full stress on logic and the conclusions that emerged are contained in the Upanishads. The Upanishads are a collection of philosophical texts that form the theoretical basis for Sanatan Dharma.
After the Upanishads, we have the Brahmasutra and Mahabharat written by Maharishi Vedvyas. Mahabharat is a vast treatise covering everything from evolution to rebirth and creation to destruction. It is like a beautiful necklace with Shrimad Bhagwad Gita forming a glittering pendant at the centre.
Gurus like Shankaracharya, Vallabhacharya and Nimbalkaracharya formed their own sects like the Advaitvad of Shankara. The differences between these sects were only a matter of interpretation and what is significant is that all the Gurus agree on “Parabrahma” (the Almighty) the creator of all life, nature, yoga and maya. They are in consensus on the Yoga of “Purush and Prakriti”.