The Supreme Divine Personality said: They speak of an eternal Ashvatth 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. – Bhagwad Gita, 15.1
Krishna speak of the eternal Ashvatth tree, which is an upside-down sacred fig (peepal) tree. Its roots are above and its branches are below. Ashvatth means that which will not remain the same even on the next day or something which is always changing. The Sanskrit word for the world, sansar is defined in the Sanskrit dictionary as sansaratiti sansarah; something that is constantly shifting.
The Sanskrit word for the world Jagat is also defined as saccharinity jagatti, that means it is a constantly moving world. The world is not just moving or constantly changing but someday it will be completely destroyed and reverted unto God. Therefore, the world we live in is temporary or Ashvatth.
Krishna further explained that this material world is like a huge Ashvatth tree for the soul. Its roots are going upwards (urdhava mulam) originating from God; nourished and supported by him. The trunk and the branches which are extending downwards (adhahshakam) encompass all the life-forms from different abodes of the material realm.
Its leaves are the Vedic mantra (chandansi), which describe rituals, ceremonies and its reward. By performing such rituals, the soul can ascend to the heavenly abodes and enjoy celestial pleasures, but eventually when the rewards deplete, they have to fall back on earth.
In this way the leaves of the Ashvatth tree nourishes the material existence of the souls and perpetuate the continuous cycle of life and death. Because of this continuity, the beginning and the end are not experienced by the souls. Hence this tree form of the world is Aayyam or eternal.
It is like the evaporation of the ocean waters which form clouds that rain down on earth, which leads to the formation of rivers. This leads again to the rivers flowing into the oceans. Likewise, the cycle of birth and death continues.
In the Vedas this tree is mentioned.
The Ashvatth tree, with its roots upwards and branches downwards is eternal. – Kathopanishad 2.3.1
Those who know this tree with its roots upwards and branches downwards will not believe that death can finish them. – Taittiriya Aranyak 1.11.5
The tree, which is described in the Vedas was to make us understand that, we are beyond the cycle of life and death and we should work on cutting this tree down. Therefore, Krishna mentions that one who understands the secret of cutting this tree of samsara is the knower of the Vedas.
The branches of the tree extend upward and downward, nourished by the three gunas with the object of the senses as tender buds. The roots of the tree hang downwards, causing the flow of the karma in the human form. Below its roots branch out causing (karmic) actions in the world of humans. – Bhagwad Gita 15.2
Krishna explains that the human form is similar to the Ashvatth tree. In the human form the soul performs karmas, which is the trunk of the tree and its branches extend upwards and downwards. Based on how the soul has performed in its past and present forms it is reborn. If it led a virtuous life, when reborn, it moves to the upward branches which denote the celestial abode of the Gandharvas, Devatas etc. In case a soul was involved in sinful acts, in the next birth it the downward branches, which are the nether regions and animal species.
Just as water irrigates a tree, the three abodes of material nature or three gunas irrigate this eternal tree of material existence. The sense objects generated by these gunas are like buds on the tree (Vishaya pravalah), which sprout causing further growth. These buds sprout creating several aerial roots of material desires. To satisfy these desires a living being has to perform karmas. These desires are insatiable and the aerial roots keep increasing which provide nourishment to this metaphorical tree. And the soul gets entangled in the web of material awareness.
The real form of this tree is not perceived in this world. It has to be cut down with the axe of detachment. The axe of detachment can only be developed with knowledge of the self. Detachment leads to stopping the growth of the tree roots. Then finally one has to seek the top of the upside-down tree, where the Lord of the creation resides. By self-surrender to the Lord, the Ashvatth tree is cut down and one attains Moksha. – Bhagwad Gita 15.3 and 4
Bhagwad Gita: Swami Mukundananda.
Aim Hrim Klim
By G3krishna – Own work, CC BY-SA 4.0, Link