Chapter 15 opens with a striking image. The entire world is compared to an upside-down Ashvattha tree — the sacred fig (peepal). Its roots reach upward, into the supreme reality. Its branches spread downward, into the world we live in. This tree, Krishna says, is imperishable.
Think of a tree standing by a riverbank. Its reflection in the water appears inverted — roots above, branches below. This world, according to Krishna, is like that reflection. The real source (the root) is above, in the divine. What we see and experience here is the reflected image.
The Vedic hymns are described as the leaves of this tree. Just as leaves make a tree look lush and full, the rituals and hymns of the Vedas sustain and elaborate this worldly existence. And the person who truly understands this entire tree — its root, its branches, its leaves — that person alone is a real knower of the Vedas.