The arrangement called four-fold varṇas, based upon the inner qualities and outer activities of people, is instituted by Me. Though the Creator of such a categorization, know Me as a Non-doer, the Imperishable.
Krishna takes the thought process to the very origin of creation, human society in particular. As the eternal Soul, he is the source of mobile and immobile creation. He identifies himself with this eternal entity, a spiritual characteristic of profound Knowers of Truth.
Human society has to be multi-splendoured in order to be amply creative and efficient. Only then its members will be able to live and move with mutuality and collectivity. To enable community life, multiple contributions from various quarters are indispensable. The fourfold categorization ensures and facilitates these.
One’s inner qualities, tendencies, and outer activities determine these. But, the ultimate source giving rise to this variety, has no preference or prejudice on this account. It is ever impartial and impersonal.