What is varna why four of them and how they differ:

Varna differ in vritti, a method of producing cash. There are 4 ways to get the pious funds, namely:
 - Receive a fixed remuneration for their labor (wages)
 - Profit
 - Collection of taxes (as well as fines and customs duties)
 - Receiving donations
These four ways of obtaining funds corresponding to the four varnas: Sudras, vaisyas, Kshatriyas and Brahmins. At the same time certain varnam match certain activities. Sudras perform assignments of those they hired vaisyas engaged in trade and agriculture (the self-determining activity), Kshatriyas are the kings, warriors, Brahmins are engaged in activities related to knowledge (they can be priests, physicians, astrologers, etc.) .

Representatives of different castes have different personal qualities, generated by their own nature and the natural way of life have different values. Sudras vital interest is stability and security vaisyas - wealth, Kshatriya - power, Brahmin - knowledge.
 
Signs of Brahmin - a possession mind, feelings of ownership, austerity, purity, contentment, placability, ingenuousness, knowledge, compassion, honesty and devotion to God.

Military valor, invincibility, endurance, strength, generosity, forbearance, forgiveness, inexhaustible vitality and truthfulness - these are signs of a Kshatriya.

The desire to improve themselves in providing material well-being and satisfaction of the senses and the ability and the constant desire to make money - these are the signs of vaisyas.

Veneration of the representatives of the upper classes, impeccable cleanliness, absence of hypocrisy, lack of propensity to theft, honesty - these are the signs of a Sudra.

Mind representative each from Varna will calm when faced with any aspect of the activity within their varna and will experience anxiety when faced with aspects of the activities of the stranger. For example, the Kshatriya not feel any anxiety from what it in the performance of their professional duties have to risk their lives. "Happy are those Kshatriyas, who suddenly falls to the opportunity to fight." However, Vaishya or Sudra would come in much confusion and would suffer if they had to fight with weapons in hand. Kshatriya, in turn, would suffer enormously if hired into the service to anyone.

Being in his varna and allows the execution of their duties up to the level of sattva, goodness, while performing the duties of others will be forced to remain in the lower gunas. And because of ignorance and passion can not be "step" in the transcendent, it can be done only from goodness.