SB 3.21.52-54

na yadā ratham āsthāya
 jaitraṁ maṇi-gaṇārpitam
visphūrjac-caṇḍa-kodaṇḍo
 rathena trāsayann aghān
sva-sainya-caraṇa-kṣuṇṇaṁ
 vepayan maṇḍalaṁ bhuvaḥ
vikarṣan bṛhatīṁ senāṁ
 paryaṭasy aṁśumān iva
tadaiva setavaḥ sarve
 varṇāśrama-nibandhanāḥ
bhagavad-racitā rājan
 bhidyeran bata dasyubhiḥ
Synonyms: 
na — not; yadā — when; ratham — the chariot; āsthāya — having mounted; jaitram — victorious; maṇi — of jewels; gaṇa — with clusters; arpitam — bedecked; visphūrjat — twanging; caṇḍa — a fearful sound just to punish the criminals; kodaṇḍaḥ — bow; rathena — by the presence of such a chariot; trāsayan — threatening; aghān — all the culprits; sva-sainya — of your soldiers; caraṇa — by the feet; kṣuṇṇam — trampled; vepayan — causing to tremble; maṇḍalam — the globe; bhuvaḥ — of the earth; vikarṣan — leading; bṛhatīm — huge; senām — army; paryaṭasi — you roam about; aṁśumān — the brilliant sun; iva — like; tadā — then; eva — certainly; setavaḥ — religious codes; sarve — all; varṇa — of varṇas; āśrama — of āśramas; nibandhanāḥ — obligations; bhagavat — by the Lord; racitāḥ — created; rājan — O King; bhidyeran — they would be broken; bata — alas; dasyubhiḥ — by rogues.
Translation: 
If you did not mount your victorious jeweled chariot, whose mere presence threatens culprits, if you did not produce fierce sounds by the twanging of your bow, and if you did not roam about the world like the brilliant sun, leading a huge army whose trampling feet cause the globe of the earth to tremble, then all the moral laws governing the varṇas and āśramas created by the Lord Himself would be broken by the rogues and rascals.
Purport: 

It is the duty of a responsible king to protect the social and spiritual orders in human society. The spiritual orders are divided into four āśramas — brahmacarya, gṛhastha, vānaprastha and sannyāsa — and the social orders, according to work and qualification, are made up of the brāhmaṇas, the kṣatriyas, the vaiśyas and the śūdras. These social orders, according to the different grades of work and qualification, are described in Bhagavad-gītā. Unfortunately, for want of proper protection by responsible kings, the system of social and spiritual orders has now become a hereditary caste system. But this is not the actual system. Human society means that society which is making progress toward spiritual realization. The most advanced human society was known as ārya; ārya refers to those who are advancing. So the question is, “Which society is advancing?” Advancement does not mean creating material “necessities” unnecessarily and thus wasting human energy in aggravation over so-called material comforts. Real advancement is advancement toward spiritual realization, and the community which acted toward this end was known as the Āryan civilization. The intelligent men, the brāhmaṇas, as exemplified by Kardama Muni, were engaged in advancing the spiritual cause, and kṣatriyas like Emperor Svāyambhuva used to rule the country and insure that all facilities for spiritual realization were nicely provided. It is the duty of the king to travel all over the country and see that everything is in order. Indian civilization on the basis of the four varṇas and āśramas deteriorated because of her dependency on foreigners, or those who did not follow the civilization of varṇāśrama. Thus the varṇāśrama system has now been degraded into the caste system.

The institution of four varṇas and four āśramas is confirmed herewith to be bhagavad-racita, which means “designed by the Supreme Personality of Godhead.” In Bhagavad-gītā this is also confirmed: cātur-varṇyaṁ mayā sṛṣṭam. The Lord says that the institution of four varṇas and four āśramas “is created by Me.” Anything created by the Lord cannot be closed or covered. The divisions of varṇas and āśramas will continue to exist, either in their original form or in degraded form, but because they are created by the Lord, the Supreme Personality of Godhead, they cannot be extinguished. They are like the sun, a creation of God, and therefore will remain. Either covered by clouds or in a clear sky, the sun will continue to exist. Similarly, when the varṇāśrama system becomes degraded, it appears as a hereditary caste system, but in every society there is an intelligent class of men, a martial class, a mercantile class and a laborer class. When they are regulated for cooperation among communities according to the Vedic principles, then there is peace and spiritual advancement. But when there is hatred and malpractice and mutual mistrust in the caste system, the whole system becomes degraded, and as stated herein, it creates a deplorable state. At the present moment, the entire world is in this deplorable condition because of giving rights to so many interests. This is due to the degradation of the four castes of varṇas and āśramas.