In plain words
The Bhagavad Gītā, the Upaniṣads and the Brahma Sūtras are the root of Indian philosophy
Ordinarily the word “Vedānta” is used as a synonym for philosophy. But Vedānta is a particular branch of the Vedic literature. The whole ‘Upaniṣadic literature’ belongs to Vedānta. The ṛks of the ‘Ṛg Veda’ are songs of joy that grasped the beauty of outer creation with inner vision and sang its fervour with love.