Vishnu Purana states that he who offers sacrifices to the almighty; he, who recites prayers, prays to him; he who does not injure living beings because Hari or Vishnu is identical with all living beings; he, who observes duly the duties of his caste is said to worship the glorious Janardana. It is said that the Brahmin, the Kshatriya, the Vaisya, the Sudra by attending to the duties prescribed by the caste, best worships Lord Vishnu. At the same time he who does not vilify another either in his presence, or in his absence, who does not speak untruth, does not injure others, pleases Keshava the best. Hari is always satisfied with him who is anxious for the welfare of all creatures, his children and his own atman. He is always pleased with a man whose mind is not sullied with anger and other passions.
Thus, it can be said that he best worships Vishnu, who observes the duties laid down by scriptures for every caste and condition of life. Vishnu Purana mentions that the duties of the Brahmins consist in making gifts, worshipping the celestials with sacrifices, studying the Vedas, performing oblations and libations with water and preserving the sacred fire. For maintenance, he may offer sacrifices for others, teach others and may accept liberal presents in a becoming manner. He must advance the well being of all and do injury to none for the greatest wealth of a Brahman consists in cherishing kind feelings towards all.
Similarly the duties of a Kshatriyas consist in making gifts to the Brahmins at pleasure, in worshipping Vishnu with various sacrifices and receiving instructions from the preceptor. His principal sources of maintenance are arms and protection of the earth. But his greatest duty consists in guarding the earth.
Vaisyas, on the other hand, has been assigned with the duties of maintenance, the feeding of the cattle, commerce and agriculture. Study, sacrifice and gift are also within the duties of the Vaisyas. Besides these they may also observe the other fixed and occasional rites. It has been stated in Vishnu Purana that the Sudra must maintain himself by attending upon the three castes, or by the profits of trade, or the earnings of mechanical labour. He my also make gifts, offer the sacrifices in which food, is presented and he may also make obsequial offerings.
Vishnu Purana further enumerates that during unavoidable circumstances a Brahmin may follow the occupation of a Kshatriya and a Kshatriya may follow the occupation of a Vaishya but in other times it is a must that every individual stays within the purview of his caste and properly carry on all the duties of caste in order to please Lord Vishnu.