The Vaishya was created for supporting the two other orders and himself by cultivation and trade, and finally it was ordained by Brahman that the Shudra should serve the three orders as a servant.
वैश्यस्तु धनधान्येन त्रीन् वर्णान् विध्यादिमान्। शूद्रो ह्येतान् परिचरेदिति ब्रह्मानुशासनम्॥ ऐल उवाच