B.G 4.13

cāturvarṇyaṁ mayā sr̥ṣṭaṁ guṇakarmavibhāgaśaḥ। tasya kartāramapi māṁ viddhyakartāramavyayam ॥13॥

The classification system of four classes, based on the duties to be performed according to one's qualities, is created by Me. Even though I am the creator of these, know Me as the non-doer, and as imperishable.

Gīta Bhāshya 4.13

Varnas are classification based on qualities. 'Brahmin', the intellectual class, is of Sātwik quality. 'Kshatriya', the warrior class, is formed by the combination of 'Sātwik' and 'Rajasic' qualities. The 'Vaisha', the business class, is formed by the combination of 'Rajasic' and 'Tamasic' qualities. The 'Shudra', the employee class, is of 'Tamasic' quality. Divisions of activities that arise due to qualities are dealt at 18.42 verse of Gita. The lord is known as 'non-doer' though He is the doer, as the nature of His actions is beyond the grasp of mortals.

ahameva hi kartā ityāha - cāturvarṇyam iti। caturvarṇasamudāyaḥ। sāttviko brāhmaṇaḥ। sāttvika rājasaḥ kṣatriyaḥ। rājasatāmaso vaiśyaḥ। tāmasaḥ śūdraḥ। iti guṇavibhāgaḥ। karmavibhāgastu- "śamo damaḥ" ityādinā vakṣyate।

Indeed, I am only the creator of the populace comprising four classes, is conveyed by the verse 'cāturvarṇyam'. Those with 'Sātwik' qualities are 'Brahmins'. Those with the combination of 'Sātwik' and 'Rājasic' qualities are 'Kshatriyas'. Those with the combination of Rājasic and Tāmasic qualities are 'Vasihyas'. Those with 'Tāmasic' qualities are 'Shūdras'. The division based on duties to be performed are stated in the verse "śamo damaḥ" (18.42), and onwards.