The example is given: just like a green bird enters into the green tree. It does not mean that the bird is mixed. No. The bird is keeping its independence as an individual. But it appears to others, those who do not see properly, that it has merged into the tree. It has actually not merged. And because it does not merge, therefore they fall down. They again come out. That is explained in the Śrīmad-Bhāgavatam that ye 'nye 'ravindākṣa vimukta-māninaḥ... Vimukta-māninaḥ. They are thinking, "Now I have become one with the Supreme." But actually, that is a false impression. Māninaḥ. Māninaḥ means actually it is not fact, but he's thinking like that. Vimukta-māninaḥ.
Why he's thinking like that? Aviśuddha-buddhayaḥ. His knowledge is not perfect. Aviśuddha. Viśuddha means perfect, and aviśuddha means not perfect. Unnecessarily he's thinking that "I have become one with the..." I remain the same part and parcel. As Kṛṣṇa says, mamaivāṁśo jīva-bhūtaḥ (BG 15.7).
Just like a big bag of rice, and you put one grain of rice. It remains one grain, but it appears that it has become one with the bag. That is not possible. Therefore Bhāgavata says, "They think like that, but actually it is not the fact." And if you question why they are thinking like that—aviśuddha-buddhayaḥ, means intelligence is not very sharp. Ye 'nye 'ravindākṣa vimukta-māninas tvayy asta-bhāvād aviśuddha-buddhayaḥ, āruhya kṛcchreṇa... āruhya kṛcchreṇa paraṁ padaṁ tataḥ patanty adhaḥ (SB 10.2.32).
These Māyāvādīs, they undergo severe penances for becoming merged into the supreme effulgence, Brahman effulgence, sāyujya-mukti. It is also not easily obtained. It also requires... So therefore, āruhya kṛcchreṇa, by undergoing... Āruhya kṛcchreṇa, by severe penances and exercises... Just like the yogis, they also exercise. Āruhya kṛcchreṇa. Kṛcchreṇa means severe practices. So they reach, they realize Brahman, but after realization also, they fall down.