Srimad Bhagavatam Canto 05, Chapter 01, Text 14

SB 5.1.14

yad-vaci tantyam guna-karma-damabhih
 sudustarair vatsa vayam suyojitah
sarve vahamo balim isvaraya
 prota nasiva dvi-pade catus-padah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
My dear boy, all of us are bound by the Vedic injunctions to the divisions of varnasrama according to our qualities and work. These divisions are difficult to avoid because they are scientifically arranged. We must therefore carry out our duties of varnasrama-dharma, like bulls obliged to move according to the direction of a driver pulling on ropes knotted to their noses.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
In this verse, the words tantyam guna-karma-damabhih are very important. We each get a body according to our association with the gunas, the qualities or modes of material nature, and we act accordingly. As stated in Bhagavad-gita, the four orders of the social system — namely brahmana, ksatriya, vaisya and sudra — are arranged according to guna and karma, their qualities and work. There is some controversy about this, however, because some say that since one receives a body according to the guna and karma of his past life, it is one’s birth that determines his social status. Others say, however, that one’s birth according to the guna and karma of his past life is not the essential consideration, since one can change his guna and karma even in this life. Thus they say that the four divisions of the social order — brahmana, ksatriya, vaisya and sudra — should be arranged according to the guna and karma of this life. This version is confirmed in Srimad-Bhagavatam by Narada Muni. While instructing Maharaja Yudhisthira about the symptoms of guna and karma, Narada Muni said that these symptoms must govern the division of society. In other words, if a person born in the family of a brahmana has the symptoms of a sudra, he should be designated as a sudra. Similarly, if a sudra has brahminical qualities, he should be designated a brahmana.
The varnasrama system is scientific. Therefore if we accept the divisions of varna and asrama according to the Vedic instructions, our lives will be successful. Unless human society is thus divided and arranged, it cannot be perfect. As stated in the Visnu Purana (3.8.9):
 purusena parah puman
visnur aradhyate pantha
 nanyat tat-tosa-karanam
“The Supreme Personality of Godhead, Lord Visnu, is worshiped by the proper execution of prescribed duties in the system of varna and asrama. There is no other way to satisfy the Supreme Personality of Godhead. One must be situated in the institution of the four varnas and asramas.” All of human society is meant to worship Lord Visnu. At the present moment, however, human society does not know that this is the ultimate goal or perfection of life. Therefore instead of worshiping Lord Visnu, people have been educated to worship matter. According to the direction of modern society, men think they can advance in civilization by manipulating matter to build skyscrapers, big roads, automobiles and so on. Such a civilization must certainly be called materialistic because its people do not know the goal of life. The goal of life is to reach Visnu, but instead of reaching Visnu, people are bewildered by the external manifestation of the material energy. Therefore progress in material advancement is blind, and the leaders of such material advancement are also blind. They are leading their followers in the wrong way.
It is best, therefore, to accept the injunctions of the Vedas, which are mentioned in this verse as yad-vaci. In accordance with those injunctions, everyone should find out whether he is a brahmana, ksatriya, vaisya or sudra and should thus be educated accordingly. Then his life will be successful. Otherwise, all of human society will be confused. If human society is divided scientifically according to varna and asrama, and if the Vedic directions are followed, one’s life, regardless of his position, will be successful. It is not that brahmanas will be elevated to the transcendental platform but not the sudras. If the Vedic injunctions are followed, all of them — brahmanas, ksatriyas, vaisyas and sudras — will be elevated to the transcendental platform, and their lives will be successful. The injunctions in the Vedas are explicit directions from the Supreme Personality of Godhead. The example cited in this verse is that bulls tied by ropes in their nostrils move according to the direction of the driver. Similarly, if we move according to the instructions of the Vedas, the perfect paths for our lives will be set. Otherwise, if we do not move in that way but act according to our whimsical ideas, our lives will be spoiled by confusion and will end in despair. Actually, because people at the present moment are not following the instructions of the Vedas, they are all confused. We must therefore accept this instruction by Lord Brahma to Priyavrata as the factual scientific direction leading to the success of life. This is also confirmed in Bhagavad-gita (16.23):
yah sastra-vidhim utsrjya
 vartate kama-karatah
na sa siddhim avapnoti
 na sukham na param gatim
If we do not live according to the injunctions of the sastras, the Vedas, we shall never achieve success in life, to say nothing of happiness or elevation to higher statuses of living.
Srimad Bhagavatam Canto 05, Chapter 01, Text 13
Srimad Bhagavatam Canto 05, Chapter 01, Text 15