O great hero! The duties of Brahmanas, Kshatriyas, Vaishyas and also of Shudras have been divided according to the qualities born of their own nature
This verse alludes to the fact that the Shudras being "born to the qualities - of their OWN nature" is justifying their treatment as the lowest of the low.
In hinduism what u get in this life is a result of karma u did in past life......
Lord Krishna speaks to Arjuna as he clarifies the origin and purpose of the caste system in sanaatana dharma (Bhagavad Gita, Chapter 4, Shloka 13).
cāturvarṇyaṃ mayā sṛṣṭaṃ guṇakarmavibhāgaśaḥ .
tasya kartāramapi māṃ viddhyakartāramavyayam .. 4\-13..
chaaturvarnyam shloka
The four-fold order was created by Me according to the divisions of quality and work. Though I am its creator, know Me to be incapable of action or change.
Cāturvarṇyaṃ: the four-fold order. The four varnas are named - Brahmin, Kshatriya, Vaishya and Shudra. They constitute the four-fold order. The three gunas - sattva, rajas and tamas - and the law of karma - these four elements were divided by Me to create the four varnas.
Sattva guna predominates in Brahmins - and they are assigned the tasks (karma) of sham, dam, tapas (meditation) etc.
Rajas guna predominates in Kshatriyas - sattva guna is secondary. Their karma is to be warriors and show bravery and tejas.
Rajas guna also predominates in Vaishyas - tamas guna is secondary. Their karma is to be farmers and traders.
Tamas guna predominates in Vaishyas - rajas guna is secondary. Their karma is to serve others.
The emphasis is on guna (aptitude) and karma (function) and not on jaati (birth). The varna or the order to which we belong is independent of sex, birth or breeding. A varna is determined by temperament and vocation - not by birth or heredity.
How well u discharge ur duties is important .......