As detailed in Bhagavad Gita Dharma (righteousness) defined as “Your right to do what is just and right and not what was destined” is that unfettered cosmic principle of life, which governs from the inside life of all living beings on mother earth including human beings.
In absence of dharma no religion could sustain of its own. In absence of dharma we just could not differentiate human beings from animals. It is governed by Dharma human beings, the highest manifest stage in cosmic life cycle behaved evenly with lower forms of life.
And hence goes the adage by Mahavira (24th Tirthankara of Jainism) “Live and let live”. Sitting on the highest pedestal of life does not make human beings superior to others, or they could indulge in indiscriminate killing of lower forms. The delicate balance on mother earth between different species is directly maintained by inherent Dharma.
In Bhagavad Gita Lord Krishna has been equated as Dharmaraja, the king of Dharma (righteousness). In the entire history of mankind there was none more pious than Lord Krishna, an avatar of his era (God manifest in human form). Amongst all human beings in the present or past Lord Krishna reigns on the top. None can beat the practice of Dharma followed by Lord Krishna.
When Arjuna refuses to fight his brethren in the battle of Mahabharata, Lord Krishna succeeds convincing Arjuna to fight the enemy head-on explaining to him that it was his Dharma to take care of his countrymen and soldiers. As a Pandava chieftain he just could not abandon them halfway. Once Arjuna realizes his Dharma, his dutifully agrees to fight the enemy.
The definition of Dharma can vary from person to person, but the cosmic principle behind Dharma always remains constant, same.
Looking at tree of Dharma we shall realize that even before advent of any religion in the world existing Dharma. Initially arrived tree of Dharma! If we cut the stem it had four compartments and precipitated wisdom of four Vedas (the first words of God invoked by mankind). The tree of Dharma grew further and advent Lord Krishna, savior messiah of his era.
Then the tree of Dharma developed its first branch and advent Mahavira (24th Tirthankara of Jainism, preceptor). 77 years later to Mahavira followed Gautama Buddha. About 423 years later to Gautama Buddha advent Jesus Christ and a few centuries later followed Prophet Mohammed. And the tree of Dharma is still growing branches and sub-branches.
Dharma is the sap of life on mother earth. It controls us from within.
Dharma of an individual and Dharma of a chieftain or a king are two different entities. One may abide by individual Dharma but fail on collective front. One may prove to be a failure as a king.
The best example of Dharma is always depicted by enlightened souls. Both Sri Ramakrishna Paramhansa and Maharshi Ramana who worked for welfare of entire mankind all the time exhibited highest level of dharma practiced by mankind. When people came to meet them, the king and the commoner had to wait in the queue. None was allowed to break the queue. Doing this Maharshi Ramana made the elite realize that in domain of God all were equal.
Dharma in Bhagavad Gita teaches mankind how to maintain equanimity in all circumstances of life and importance of practicing spirituality to reach cosmic end of life, state of self realization, god realization. It is Dharma that tells us importance of spiritual journey.
Furthermore it is Dharma that tells human beings not to quit family midway in search of God. Just by touching feet of wife and child Siddhartha Gautama did not absolve himself of karma. We do not burn karma that way. We have to seek permission of family before indulging in spirituality. Only when all are agreeable we can quit family life in search of cosmic truths of life.