Here the material world is described as a tree whose roots are upwards and branches are below. We have experience of a tree whose roots are upward: if one stands on the bank of a river or any reservoir of water, he can see that the trees reflected in the water are upside down. The branches go downward and the roots upward. Similarly, this material world is a reflection of the spiritual world. The material world is but a shadow of reality. In the shadow there is no reality or substantiality, but from the shadow we can understand that there are substance and reality. In the desert there is no water, but the mirage suggests that there is such a thing as water. In the material world there is no water, there is no happiness, but the real water of actual happiness is there in the spiritual world.
The duration of the material universe is limited. It is manifested in cycles of kalpas. A kalpa is a day of Brahma, and one day of Brahma consists of a thousand cycles of four yugas, or ages: Satya, Treta, Dvapara and Kali. The cycle of Satya is characterized by virtue, wisdom and religion, there being practically no ignorance and vice, and the yuga lasts 1,728,000 years. In the Treta-yuga vice is introduced, and this yuga lasts 1,296,000 years. In the Dvapara-yuga there is an even greater decline in virtue and religion, vice increasing, and this yuga lasts 864,000 years. And finally in Kali-yuga (the yuga we have now been experiencing over the past 5,000 years) there is an abundance of strife, ignorance, irreligion and vice, true virtue being practically nonexistent, and this yuga lasts 432,000 years. In Kali-yuga vice increases to such a point that at the termination of the yuga the Supreme Lord Himself appears as the Kalki avatara, vanquishes the demons, saves His devotees, and commences another Satya-yuga. Then the process is set rolling again. These four yugas, rotating a thousand times, comprise one day of Brahma, and the same number comprise one night. Brahma lives one hundred of such “years” and then dies. These “hundred years” by earth calculations total to 311 trillion and 40 billion earth years. By these calculations the life of Brahma seems fantastic and interminable, but from the viewpoint of eternity it is as brief as a lightning flash. In the Causal Ocean there are innumerable Brahmas rising and disappearing like bubbles in the Atlantic. Brahma and his creation are all part of the material universe, and therefore they are in constant flux
There is no ready experience in this world of a tree situated with its branches down and its roots upward, but there is such a thing. That tree can be found beside a reservoir of water. We can see that the trees on the bank reflect upon the water with their branches down and roots up. In other words, the tree of this material world is only a reflection of the real tree of the spiritual world. This reflection of the spiritual world is situated on desire, just as a tree’s reflection is situated on water. Desire is the cause of things’ being situated in this reflected material light. One who wants to get out of this material existence must know this tree thoroughly through analytical study. Then he can cut off his relationship with it.
The extra roots coming out of it were compared to the activities of the living entities, some auspicious, some inauspicious. In the Ninth Chapter, also, the devas, or godly, and the asuras, the ungodly, or demons, were explained. Now, according to Vedic rites, activities in the mode of goodness are considered auspicious for progress on the path of liberation, and such activities are known as daivi prakriti, transcendental by nature. Those who are situated in the transcendental nature make progress on the path of liberation. For those who are acting in the modes of passion and ignorance, on the other hand, there is no possibility of liberation. Either they will have to remain in this material world as human beings, or they will descend among the species of animals or even lower life forms. In this Sixteenth Chapter the Lord explains both the transcendental nature and its attendant qualities and the demoniac nature and its qualities. He also explains the advantages and disadvantages of these qualities.