Gita (18:41) O Scorcher of Foes! the duties of Brahmins, Kshatriyas, and Vaishyas, as also of Shudras, are (inborn and diverse) according to the gunas uppermost in their natures.

The inner, mystical caste system is a practical way for us to gauge our level of awareness and the play of the gunas within us. Krishna helps put these stages of evolution of consciousness into the right perspective for us.