In plain words
The ‘Sāma chant’ is a treasury of supremely lovely words, fit to be sung and praised. A compendium of the secrets of this world and the next took the form of the ‘Atharvaṇa’. The yajñas and yāgas that are good and meritorious karmas, and the mantras that belong to ritual, came into the ‘Yajur Veda’. The Vedic literature, spread out in this way in four parts, again has four branches. All of these are called ‘Vidyās’. The mantra portion, the Brāhmaṇa portion, the Āraṇyaka, and the Upaniṣad portion. The mantra portion is also called the Saṃhitā portion. In it all the mantras are gathered together in brief.