Bhagavad Gita: Chapter 15, Verse 1

श्रीभगवानुवाच |
ऊर्ध्वमूलमध:शाखमश्वत्थं प्राहुरव्ययम् |
छन्दांसि यस्य पर्णानि यस्तं वेद स वेदवित् || 1||

śhrī-bhagavān uvācha
ūrdhva-mūlam adhaḥ-śhākham aśhvatthaṁ prāhur avyayam
chhandānsi yasya parṇāni yas taṁ veda sa veda-vit

śhrī-bhagavān uvāchathe Supreme Divine Personality said; ūrdhva-mūlamwith roots above; adhaḥdownward; śhākhambranches; aśhvatthamthe sacred fig tree; prāhuḥthey speak; avyayameternal; chhandānsiVedic mantras; yasyaof which; parṇānileaves; yaḥwho; tamthat; vedaknows; saḥhe; veda-vitthe knower of the Vedas


BG 15.1: The Supreme Divine Personality said: They speak of an eternal aśhvatth tree with its roots above and branches below. Its leaves are the Vedic hymns, and one who knows the secret of this tree is the knower of the Vedas.


The word aśhvatth means that which will not remain the same until even the next day.  This world is also aśhvatth, as it is constantly changing.  The Sanskrit dictionary defines the world in the following manner: sansaratīti sansāraḥ  “That which is constantly shifting is Sansar (a Sanskrit word for world).”  Gachchhatīti jagat  “That which is always moving is Jagat (another Sanskrit word for world).”  Not only is the world always changing, but it will also be annihilated and absorbed back into God one day.  Thus, everything in it is temporary, or aśhvatth.   

Aśhvatth also has another meaning.  It is the peepal tree (sacred fig), of the banyan tree family.  Shree Krishna explains that, for the soul, this material world is like a huge aśhvatth tree.  Generally, trees have their roots below and branches above.  But this tree has its roots above (ūrdhva-mūlam), i.e. it has originated from God, it is based in Him, and is supported by Him.  Its trunk and branches extend downward (adhaḥ-śhākham), encompassing all the life-forms in all the abodes of the material realm. 

The leaves of the tree are those Vedic mantras (chhandānsi) that deal with ritualistic ceremonies and their rewards.  They provide the juice for nourishing the tree of material existence.  By engaging in the fruitive ritualistic yajñas described in these Vedic mantras, the soul goes to the heavenly abodes to enjoy celestial pleasures, only to descend back to earth when the meritorious deeds are depleted.  Thus, the leaves of the tree nourish it by perpetuating the cycle of life and death.  This tree in the form of the world is called eternal (avyayam) because its flow is continuous, and its beginning and end are not experienced by the souls.  Just as the water of the sea evaporates to form clouds, then rains down on earth and merges into the sea again in a continuous process, similarly the cycle of life and death is perpetual. 

The Vedas also mention this tree:

ūrdhvamūlo ’vākśhākha eṣho ’śhvatthaḥ sanātanaḥ   (Kaṭhopaniṣhad 2.3.1) 

“The aśhvatth tree, with its roots upward and branches downward is eternal.”

ūrdhvamūlaṁ arvākśhākhaṁ vṛikṣhaṁ yo samprati

na sa jātu janaḥ śhraddhayātmṛityutyurmā mārayaditi (Taittirīya Āraṇyak 1.11.5)

“Those who know this tree with its roots upward and branches downward will not believe that death can finish them.” 

The Vedas describe this tree with the intention that we should endeavor to chop it down.  Thus, Shree Krishna says that one who knows the secret of cutting down this tree of samsara is the knower of the Vedas (veda vit).