Paras tasmāt tu bhāvo 'nyo 'vyakto 'vyaktāt sanātanaḥ (BG 8.20), you'll find in the Bhagavad-gītā. There is another nature. This nature, what you see, the sky, a round dome, this, that, above that, there are layers of five elements again. This is the covering. Just like you have seen the coconut. There is hard covering, and within the covering there is water. Similarly, within this covering. . . And outside the covering there are five layers, thousand times bigger than the one another: water layer, air layer, fire layer. So you have to penetrate all these layers. Then you will get the spiritual world. All these universes, unlimited number, koṭi. Yasya prabhā prabhavato jagad-aṇḍa-koṭi (Bs. 5.40). Jagad-aṇḍa means the universe. Koṭi, many millions clustered together, that is material world. And beyond that material world there is spiritual world, another sky. That is also sky. That is called paravyoma. So by your sense perception you cannot estimate even what is there in the moon planet or sun planet, this planet, within this universe. How you can understand the spiritual world by speculation? This is foolishness.
Therefore śāstra says, acintyāḥ khalu ye bhāvā na tāṁs tarkeṇa yojayet (Skanda Purāṇa). Acintya, which is inconceivable, beyond your sense perception, don't try to argue and understand it and speculate. This is foolishness. It is not possible. Therefore we have to go to the guru. Tad-vijñānārthaṁ sa gurum evābhigacchet, samit-pāṇiḥ śrotriyaṁ brahma-niṣṭham (MU 1.2.12). This is the process. But the demons, they do not know this is the process. They speculate; they manufacture. Simply by jugglery of words they manufacture their truth. No. Satyaṁ paraṁ dhīmahi. That is in the Bhāgavatam, you'll find. And what is satyam? Janmādy asya yato 'nvayād itarataś cārtheṣv abhijñaḥ svarāṭ tene brahma hṛdā. . . (SB 1.1.1). Everything is there.
So don't remain in the ignorant stage of life. That is called śūdra. Try to become brāhmaṇa. That is the meaning. It is not prohibited that one cannot become brāhmaṇa. No, one can become brāhmaṇa. If he gets association of a brāhmaṇa, if he agrees to be trained up by a brāhmaṇa, he can become brāhmaṇa. And brāhmaṇa means brahma jānāti iti brāhmaṇa, not by birth. Anyone who has full knowledge of the Supreme, he is brāhmaṇa. Janmanā jāyate śūdraḥ. By birth everyone is śūdra. Even if he's born in a brāhmaṇa family he is śūdra. Janmanā jāyate śūdraḥ saṁskārād bhaved dvijaḥ. The saṁskāra means purification. That is satyaṁ śaucam. But the asuras, they do not want to be purified. They want to remain in the degraded stage of life. That is the difficulty. Otherwise it doesn't matter what he is, which family he's born. It doesn't matter.
Kṛṣṇa says, you'll find, māṁ hi pārtha vyapāśritya ye 'pi syuḥ pāpa-yonayaḥ (BG 9.32). Pāpa-yoni. To take birth low-grade family, or animal family, these are called pāpa-yoni. Kṛṣṇa says that it doesn't matter if one is born in the pāpa-yoni, low-grade family. It doesn't matter. Māṁ hi pārtha vyapāśritya ye 'pi syuḥ pāpa-yonayaḥ. In the human society, striyaḥ śūdrās tathā vaiśyāḥ, even woman and śūdra and vaiśya, they are also taken in the category of pāpa-yoni. Pāpa-yoni means their intelligence is not very sharp. That is called pāpa-yoni. And a brāhmaṇa means to become very, very highly intellectual. That is called brāhmaṇa. Because he'll understand Brahman.