When the conditioned soul decides to associate with the material qualities, he becomes contaminated by those qualities.
“When the conditioned soul decides to associate with the material qualities, he becomes contaminated by those qualities. As stated in the Gītā (13.22), kāraṇaṁ guṇa-saṅgo ’sya sad-asad-yoni-janmasu. For example, in the presence of a seductive woman, a man may give in to his lower instincts and try to enjoy sex with her. By his deciding to associate with the lower qualities of nature, those qualities manifest in him very powerfully. He is overwhelmed with lust and driven to try again and again to satisfy his burning desire. Because his mind has been infected by lust, all that he does, thinks and speaks will be influenced by his strong attachment to sex. In other words, by choosing to associate with the lusty qualities of nature, he has caused them to powerfully manifest within himself, and eventually those lusty qualities themselves will cause him to accept another material body suitable for affairs governed by those qualities.
The lower qualities, such as lust, greed, anger and envy, are abudha-liṅga-bhāvāḥ, symptoms of ignorance. Indeed, as indicated by Śrīla Śrīdhara Svāmī in his commentary, the manifestation of the modes of nature is synonymous with the manifestation of a particular material body. It is clearly explained throughout the Vedic literature that the conditioned soul receives a particular body, gives it up and then accepts another simply because of his involvement with the modes of nature (kāraṇaṁ guṇa-saṅgo ’sya). Thus to say that one is participating in the modes of nature is to say that one is accepting particular types of bodies suitable for the particular material qualities one is involved with.”
Source:A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Tenth Canto, Chapter 27 – Text 05
