According to Vedic texts, varnashrama-dharma is not a man-made system but refers to natural classifications that appear to various degrees in all human societies. Individuals have different innate tendencies for work and exhibit a variety of personal qualities. 

चातुर्वर्ण्यं मया सृष्टं गुणकर्मविभागशः ।

तस्य कर्तारमपि मां विद्ध्यकर्तारमव्ययम् ॥ १३ ॥

cātur-varṇyaṁ mayā sṛṣṭaṁ

guṇa-karma-vibhāgaśaḥ

tasya kartāram api māṁ

viddhy akartāram avyayam

Translation

According to the three modes of material nature and the work associated with them, the four divisions of human society are created by Me. And although I am the creator of this system, you should know that I am yet the nondoer, being unchangeable.  Bhagavad Gita 4.13

There are also natural phases in life, when it is easier and more rewarding to perform certain activities. The Vedas teach that individuals best realise their potential by taking into account such natural arrangements, and that society should be structured and organised accordingly.

Each varna and ashram has its own specified dharma. What may be desirable for one section of society may be degrading for another. For example, absolute non-violence, which includes refraining from animal sacrifice, is essential for the priestly class but considered wholly unworthy of a kshatriya (warrior). Generating wealth and producing children are essential for householders, but intimate contact with money and women is spiritually suicidal for the renunciate. Underlying all these apparent differences is the common goal of advancing in spiritual life based on sanatana-dharma. Without the spiritual equality and sense of service inherent in sanatana­dharma, varnashrama-dharma tends to degrade into the rigid and exploitative caste system.

Key Points

Varnashrama-dharma – duties performed according to the system of four varnas (social divisions) and four ashrams (stages in life).

Focus is on responsibilities (which naturally fulfil the rights of others).

Four varnas – brahmanas (priests, teachers, and intellectuals), kṣatriyas (police, army, and administration), vaiśyas (farmers, merchants, and business people), śudras (artisans and workers).

Four ashrams – student life, household life, retirement, and renunciation.

Useful Analogy - The social body

(The social body and its components are likened to the human form).

Society is compared to a body with the brahmanas as the head, kṣatriyas as the arms, vaishyas as the belly (or thighs) and the śudras as the legs.  Social functions are determined according to this analogy. For example, the brahmanas are the eyes and mouth of society. They provide a spiritual vision for society and teach people accordingly. Just as the arms are raised to defend the body, the kshatriya’s main duty is to protect society. The vaiśya’s main duty is material nourishment, and the śudra supports all other sections of society.

The  are sometimes related to the same metaphor, with the successive stages of student life, household life, retirement and renunciation represented by the legs, belly, arms and head respectively.