In the Gita, Sri Krishna emphasizes Svadharma, one’s own dharma. The word ‘dharma’ is really untranslatable. ‘Religion,’ ‘duty,’ ‘righteousness,’ and the other English equivalents give only a partial meaning. Dharma is derived from the root ‘dhri’, meaning to hold or sustain. The word signifies the attitude behind a man’s action or duty that sustains him in his present stage of evolution and also helps him to realize his ultimate destiny.
The dharma of a man is determined by his past experiences and tendencies. The beginningless Soul assumes different forms in different births for the gaining of experience. The works performed in every birth leave impressions, which are stored up in the subconscious mind and are not destroyed with the death of the body. When the Soul assumes a new body, these impressions begin to operate. Thus they form his ‘svabhava’, or character; they determine his dharma – his duty, his religion, his sense of right and wrong.
Education and environment only help a man to manifest what he has inherited from his own past. ... So a man’s dharma is the basis of his thought and action; he cannot get rid of it any more than a dreaming person can get rid of his dream. To try to act against one’s dharma is to do violence to one’s nature. The duty determined by a man’s dharma is his natural duty.
That is the only real thing for him; all other duties are alien to his nature, imposed from outside and therefore sources of confusion.
(Source – Swami Nikhilananda – Introduction to Bhagavad Gita)