B.G 4.13

चातुर्वर्ण्यं मया सृष्टं गुणकर्मविभागशः। तस्य कर्तारमपि मां विद्ध्यकर्तारमव्ययम् ॥१३॥

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.

अहमेव हि कर्ता इत्याह - चातुर्वर्ण्यम् इति। चतुर्वर्णसमुदायः। सात्त्विको ब्राह्मणः। सात्त्विक राजसः क्षत्रियः। राजसतामसो वैश्यः। तामसः शूद्रः। इति गुणविभागः। कर्मविभागस्तु- "शमो दमः" इत्यादिना वक्ष्यते।

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.