The material nature is divided into three modes: sattva-guṇa, tamo-guṇa, rajo-guṇa. So to become within the material nature, under the control of the material nature, means to accept one of these guṇas, sattva-guṇa, rajo-guṇa, tamo-guṇa. So if you accept this sattva-guṇa, the brahminical qualification, satyaṁ śamo dama titikṣā ārjavaṁ kṣāntiḥ, jñānaṁ vijñānam āstikyaṁ brahma-karma svabhāva . . . (BG 18.42). If you associate with the brahminical qualification, then you get nicer body. Ūrdhvaṁ gacchanti sattva-sthāḥ (BG 14.18). Those who are associating with the sad-guṇa, they are also described. Sad-guṇa means satyaṁ śamo dama titikṣā ārjavaṁ kṣāntiḥ, jñānaṁ vijñānam āstikyaṁ brahma-karma . . . this is brahma-karma. So tapasya means come to the brahma-karma, not to the śūdra-karma. Kāraṇaṁ guṇa-saṅgo 'sya (BG 13.22). Don't associate with the śūdra qualification. Now, what is the śūdra qualification? Paricaryātmakaṁ kāryaṁ śūdra-karma svabhāva-jam (BG 18.44). You are highly educated, but your desire is how to get a service. Paricarya . . . I am highly educated, but unless I render service to somebody else like a dog, I am not recognized. This is called śūdra-karma. Why a brāhmaṇa, kṣatriya, vaiśya should search after service? Therefore in this Kali-yuga it is said, kalau śūdraḥ sambhavaḥ: "Kalau, in this Kali-yuga, everyone is almost śūdras." There is lack of brāhmaṇa. There is lack of kṣatriya and vaiśya.
So in Bhagavad-gītā we'll find all the solution of the human problems. All the solution. Cātur-varṇyaṁ mayā sṛṣṭaṁ guṇa-karma-vibhāgaśaḥ (BG 4.13). Unless you divide the whole human society into four divisions—the brāhmaṇa, kṣatriya, vaiśya and śūdra . . . you must have to divide. You cannot say: "Classless society." That is useless society. Classless society means useless society. There must be an intelligent high class, ideal class of men to see that, "Here is human civilization." That is brāhmaṇa. Cātur-varṇyaṁ mayā sṛṣṭaṁ guṇa-karma . . . unless people see the ideal men, how they will follow? Yad yad ācarati śreṣṭhaḥ, lokas tad anuvartate (BG 3.21). The brāhmaṇa is compared with the brain of the body. Unless there is brain, what is the use of these hands and legs? If one's brain is cracked, madman, he cannot do anything.