Śrīla Rāmānujācārya writes in his book Vedārtha-saṅgraha:
evaṁ-vidha-parābhakti-svarūpa-jñāna-viśeṣasyotpādakaḥ pūrvoktāharahar upacīyamāna-jñāna-pūrvaka-karmānugṛhīta-bhakti-yoga eva; yathoktaṁ bhagavatā parāśareṇa — varṇāśrameti. nikhila-jagad-uddhāraṇāyāvanitale ’vatīrṇaṁ para-brahma-bhūtaḥ puruṣottamaḥ svayam etad uktavān — “svakarma-nirataḥ siddhiṁ yathā vindati tac chṛṇu” “yataḥ pravṛttir bhūtānāṁ yena sarvam idaṁ tatam/ svakarmaṇā tam abhyarcya siddhiṁ vindati mānavaḥ.”
Translation:
The cause of such kind of knowledge, which is nothing but of the nature of para (transcendental) bhakti is certainly Bhakti-yoga or devotional service. Such devotional service is preceded by ever-increasing knowledge as it’s been said previously. Also, it has been followed according to one’s karma or prescribed duties.
In the Viṣṇu Purāṇa (3.8.9), the great sage Parāśara Muni has recommended:
varṇāśramācāravatā puruṣeṇa paraḥ pumān
viṣṇur ārādhyate panthā nānyat tat-toṣa-kāraṇam
“The Supreme Personality of Godhead, Lord Viṣṇu, is worshiped by the proper execution of prescribed duties in the system of varṇa and āśrama. There is no other way to satisfy the Lord.”
In the land of Bhārata-varṣa, the institution of varṇāśrama-dharma may be easily adopted. At the present moment, certain demoniac sections of the population of Bhārata-varṣa are disregarding the system of varṇāśrama-dharma. Because there is no institution to teach people how to become brāhmaṇas, kṣatriyas, vaiśyas and śūdras or brahmacārīs, gṛhasthas, vānaprasthas and sannyāsīs, these demons want a classless society. This is resulting in chaotic conditions. In the name of secular government, unqualified people are taking the supreme governmental posts. No one is being trained to act according to the principles of varṇāśrama-dharma, and thus people are becoming increasingly degraded and are heading in the direction of animal life. The real aim of life is liberation, but unfortunately the opportunity for liberation is being denied to people in general, and therefore their human lives are being spoiled. The Kṛṣṇa consciousness movement, however, is being propagated all over the world to reestablish the varṇāśrama-dharma system and thus save human society from gliding down to hellish life.
To deliever the whole world, The Supreme Personalility of Godhead, the Supreme brahma, Purusottama, having appeared on this planet earth, has declared it in His own words:
sve sve karmaṇy abhirataḥ saṁsiddhiṁ labhate naraḥ
sva-karma-nirataḥ siddhiṁ yathā vindati tac chṛṇu (BG 18.45)yataḥ pravṛttir bhūtānāṁ yena sarvam idaṁ tatam
sva-karmaṇā tam abhyarcya siddhiṁ vindati mānavaḥ(BG 18.46)
Translation of BG 18.45, 18.46
By following his qualities of work, every man can become perfect. Now please hear from Me how this can be done.
By worship of the Lord, who is the source of all beings and who is all-pervading, a man can attain perfection through performing his own work.