CC Madhya 8.57

prabhu kahe, — “paḍa śloka sādhyera nirṇaya”
rāya kahe, — “sva-dharmācaraṇe viṣṇu-bhakti haya”
Word for word: 
prabhu kahe — Lord Śrī Caitanya Mahāprabhu said; paḍa — just recite; śloka — a verse from the revealed scriptures; sādhyera — of the aim of life; nirṇaya — an ascertainment; rāya kahe — Rāmānanda Rāya replied; sva-dharma-ācaraṇe — by executing one’s occupational duty; viṣṇu-bhakti — devotional service to Lord Viṣṇu; haya — there is.
Translation: 
Śrī Caitanya Mahāprabhu ordered Rāmānanda Rāya, “Recite a verse from the revealed scriptures concerning the ultimate goal of life.”
Purport: 

Rāmānanda replied, “If one executes the prescribed duties of his social position, he awakens his original Kṛṣṇa consciousness.

In this connection, Śrī Rāmānujācārya states in the Vedārtha-saṅgraha that devotional service is naturally very dear to the living entity. Indeed, it is life’s goal. This devotional service is supreme knowledge, or Kṛṣṇa consciousness, and it brings detachment from all material activity. In the transcendental position, a living being can perfectly acknowledge the superiority of serving the Supreme Lord. The devotees attain the Supreme Lord only by devotional service. Having such knowledge, one engages in his occupational duty, and that is called bhakti-yoga. By performing bhakti-yoga, one can rise to the platform of pure devotional service.

A great saint, the father of Śrīla Vyāsadeva, Parāśara Muni, has specifically mentioned that devotional service to the Lord can ultimately be awakened in human society by the discharge of duties in accordance with the varṇāśrama system. The Supreme Personality of Godhead instituted varṇāśrama-dharma to give human beings a chance to return home, back to Godhead. The Supreme Personality of Godhead, Lord Śrī Kṛṣṇa, who is known in the Bhagavad-gītā as Puruṣottama — the greatest of all personalities — personally came and declared that the institution of varṇāśrama-dharma was founded by Him. As stated in the Bhagavad-gītā (4.13):

cātur-varṇyaṁ mayā sṛṣṭaṁguṇa-karma-vibhāgaśaḥ
tasya kartāram api māṁ
viddhy akartāram avyayam

Elsewhere in the Bhagavad-gītā (18.45-46) the Lord says:

sve sve karmaṇy abhirataḥsaṁsiddhiṁ labhate naraḥ
sva-karma-nirataḥ siddhiṁ
yathā vindati tac chṛṇu

yataḥ pravṛttir bhūtānāṁyena sarvam idaṁ tatam
sva-karmaṇā tam abhyarcya
siddhiṁ vindati mānavaḥ

Human society should be divided into four divisions — brāhmaṇa, kṣatriya, vaiśya and śūdra — and everyone should always engage in his occupational duty. The Lord says that those engaged in their occupational duty can attain perfection simply by rendering loving devotional service to the Lord while executing their particular duty. Actually the modern ideal of a classless society can be introduced only by Kṛṣṇa consciousness. Let men perform their occupational duty, and let them give their profits to the service of the Lord. In other words, one can attain the perfection of life by discharging one’s occupational duty and employing the results in the service of the Lord. This method is confirmed by great personalities like Bodhāyana, Taṅka, Dramiḍa, Guhadeva, Kapardi and Bhāruci. It is also confirmed by the Vedānta-sūtra.