Complex sentence: The Shudra, states Marvin Davis, are not required to learn the Vedas, is not "twice born" ("Dvija "), and their occupational sphere is service ("seva") of the other three varna.
Split into simpler sentences: The Shudra, states Marvin Davis, are not required to learn the Vedas. They were not "twice born" ("Dvija "), and their occupational sphere stated as service ("seva") of the other three varna.