Srimad-Bhagavatam: Canto 6 - Chapter 1 - Verse 51
Sanskrit:
तदेतत्षोडशकलं लिङ्गं शक्तित्रयं महत् ।धत्तेऽनुसंसृतिं पुंसि हर्षशोकभयार्तिदाम् ॥ ५१ ॥
ITRANS:
tad etat ṣoḍaśa-kalaṁliṅgaṁ śakti-trayaṁ mahatdhatte ’nusaṁsṛtiṁ puṁsiharṣa-śoka-bhayārtidām
Translation:
The subtle body is endowed with sixteen parts — the five knowledge-acquiring senses, the five working senses, the five objects of sense gratification, and the mind. This subtle body is an effect of the three modes of material nature. It is composed of insurmountably strong desires, and therefore it causes the living entity to transmigrate from one body to another in human life, animal life and life as a demigod. When the living entity gets the body of a demigod, he is certainly very jubilant, when he gets a human body he is always in lamentation, and when he gets the body of an animal, he is always afraid. In all conditions, however, he is actually miserable. His miserable condition is called saṁsṛti, or transmigration in material life.
Purport:
The sum and substance of material conditional life is explained in this verse. The living entity, the seventeenth element, is struggling alone, life after life. This struggle is called saṁsṛti, or material conditional life. In Bhagavad-gītā it is said that the force of material nature is insurmountably strong (daivī hy eṣā guṇa-mayī mama māyā duratyayā). Material nature harasses the living entity in different bodies, but if the living entity surrenders to the Supreme Personality of Godhead, he becomes free from this entanglement, as confirmed in Bhagavad-gītā (mām eva ye prapadyante māyām etāṁ taranti te). Thus his life becomes successful.