In plain words
Through forgetting this very Dharma, the earth takes on a form wholly empty of Dharma. It keeps falling into many hardships, sorrows and griefs. So in such conditions we must make Dharma grow, nourish the knowledge that is the root and basis of Dharma as well, and take a vow to restore Dharma once again in the land of Bhārata.
In the Bhagavad Gītā too, at its very start, ‘dharmakṣetre kurukṣetre samavetā yuyutsavaḥ’; when many were asked what the essence of the Bhagavad Gītā is, many have gone on explaining this Bhagavad Gītā well in many ways: that karma is foremost in it, that yoga is most important, that Jñāna is most important, that Bhakti is most important. If we are to make out a single form, the feet and the head are most important. When the feet and the head are not to be had, from the trunk we can make out nothing at all. So in the very first śloka,
On the field of Dharma, on the field of Kuru, gathered and eager to fight, my sons and the sons of Pāṇḍu, what did they do, O Sañjaya?
the first word is Dharma. And at the end,
Where there is Kṛṣṇa, the Lord of yoga, where there is Pārtha, Dhanañjaya, there are fortune, victory, prosperity and sure conduct: so I hold,
the last word is ‘mama’. When we join these two, it has gone on teaching ‘mama dharma’. So it has also gone on teaching that each person must recognise their own Dharma and act by it. The householder must follow the Dharma of the householder, the vānaprastha the Dharma of the vānaprastha, the sannyāsī the Dharma of the sannyāsī, the brahmacārī the Dharma of the brahmacārī. The Dharma fit for each belongs to that one alone; one person's cannot belong to another. So it went on, keeping such rules, teaching them and reflecting on them.
The root and basis of everything is mama dharma. There is no other Dharma in the world beyond this mama dharma. Once a German philosopher named Fredernich was writing a book called ‘The Power of the Will’. While he was writing it, by good fortune, this mama dharma came into his hands.