What determines one's duty in modern times

Since the caste that one is born into has little relevance today, and one's nature or behavior is not only governed by the caste that one is born into, duty is governed by one's individual nature and talents, as well as the type of action that is required at that time to benefit the world most. For example, peacefulness, self-control, austerity, purity, tolerance, honesty, knowledge, wisdom and religiousness are qualities of the brahmanas. A person who has these qualities is a brahmana, irrespective of the caste of his birth. These qualities are defined, however the nature of work is not. Hence, the brahmana can be doing work that is traditionally associated with a kshatriya (military and politics), vaisya (trade and business) or shudra (service and labor), but he can retain the qualities of peacefulness, self-control, honesty etc. The qualities make him a brahmana, not his birth or the nature of work. If the brahmana has talents in leadership and courage, he can take on an occupation that is traditionally associated with a kshatriya. Even if he is a peaceful person, but if the rights of innocents are at stake, and the need of the hour is to defend righteousness, a brahmana can take up arms to protect the innocent and bring about peace in the region. If he has talents in business and if enterprise is required for progress of society, he can do business. He has to choose the occupation in which he has the talents to be of service to others in the best possible manner, while retaining an attitude of self-control and purity.

Lord Krishna had the qualities of peacefulness, self-control, austerity, purity, tolerance, honesty, knowledge, wisdom and religiousness. He was born into a Kshatriya family, and raised by a Vaisya family that owned and protected cows. However he had all the best qualities of people from each of the castes. When Lord Krishna does any work (e.g., that of a learned priest, a warrior, a cowherd, or a charioteer), he does it to the best of his ability, and with love. He does not hesitate to even do the work that is typically associated with a person of a lower caste (that of a charioteer) out of love for his devotee Arjuna and for the sake of dharma (righteousness). He knew that he had to do a charioteer's work if he had to help Arjuna and the Pandavas win for the sake of dharma . A model person should be like Krishna. He should have the best qualities of people from each of the castes and should not identify with any caste, attach much significance to a person's caste of birth, or be partial to people from any of the castes. He must use his talents and best qualities to the best of his abilities and perform actions that will be of most benefit to the world.