Now, coming to your beautiful question, first let me quote what Sri Aurobindo said about Sanatana Dharma.
‘I was not only to understand intellectually but to realise what Srikrishna demanded of Arjuna and what He demands of those who aspire to do His work, to be free from repulsion and desire, to do work for Him without the demand for fruit, to renounce self-will and become a passive and faithful instrument in His hands, to have an equal heart for high and low, friend and opponent, success and failure, yet not to do His work negligently. I realised what the Hindu religion meant. We speak often of the Hindu religion, of the Sanatana Dharma, but few of us really know what that religion is. Other religions are preponderatingly religions of faith and profession, but the Sanatana Dharma is life itself; it is a thing that has not so much to be believed as lived. This is the dharma that for the salvation of humanity was cherished in the seclusion of this peninsula from of old. It is to give this religion that India is rising. She does not rise as other countries do, for self or when she is strong, to trample on the weak. She is rising to shed the eternal light entrusted to her over the world. India has always existed for humanity and not for herself and it is for humanity and not for herself that she must be great.
Therefore this was the next thing He pointed out to me,—He made me realise the central truth of the Hindu religion. He turned the hearts of my jailers to me and they spoke to the Englishman in charge of the jail, “He is suffering in his confinement; let him at least walk outside his cell for half an hour in the morning and in the evening.” So it was arranged, and it was while I was walking that His strength again entered into me. I looked at the jail that secluded me from men and it was no longer by its high walls that I was imprisoned; no, it was Vasudeva who surrounded me. I walked under the branches of the tree in front of my cell, but it was not the tree, I knew it was Vasudeva, it was Srikrishna whom I saw standing there and holding over me His shade. I looked at the bars of my cell, the very grating that did duty for a door and again I saw Vasudeva. It was Narayana who was guarding and standing sentry over me. Or I lay on the coarse blankets that were given me for a couch and felt the arms of Srikrishna around me, the arms of my Friend and Lover. This was the first use of the deeper vision He gave me. I looked at the prisoners in the jail, the thieves, the murderers, the swindlers, and as I looked at them I saw Vasudeva, it was Narayana whom I found in these darkened souls and misused bodies……
But what is the Hindu religion? What is this religion which we call Sanatana, eternal? It is the Hindu religion only because the Hindu nation has kept it, because in this peninsula it grew up in the seclusion of the sea and the Himalayas, because in this sacred and ancient land it was given as a charge to the Aryan race to preserve through the ages. But it is not circumscribed by the confines of a single country, it does not belong peculiarly and for ever to a bounded part of the world. That which we call the Hindu religion is really the eternal religion, because it is the universal religion which embraces all others. If a religion is not universal, it cannot be eternal. A narrow religion, a sectarian religion, an exclusive religion can live only for a limited time and a limited purpose. This is the one religion that can triumph over materialism by including and anticipating the discoveries of science and the speculations of philosophy. It is the one religion which impresses on mankind the closeness of God to us and embraces in its compass all the possible means by which man can approach God. It is the one religion which insists every moment on the truth which all religions acknowledge, that He is in all men and all things and that in Him we move and have our being. It is the one religion which enables us not only to understand and believe this truth but to realise it with every part of our being. It is the one religion which shows the world what the world is, that it is the lila of Vasudeva. It is the one religion which shows us how we can best play our part in that lila, its subtlest laws and its noblest rules. It is the one religion which does not separate life in any smallest detail from religion, which knows what immortality is and has utterly removed from us the reality of death.’
Source: CWSA Vol. 08: Karmayogin: > Uttarpara Speech
Link: https://incarnateword.in/cwsa/08/uttarpara-speech#p4
The word Sanatana means that which is Eternal. In other words, it has no beginning at a point in time, and accordingly it does end as well. Secondly, it is Universal and all-encompassing. Just as it is not limited by Time, it is not limited by Space either. Being universal, it can give birth to and absorb all other paths, sects, religions cults within in as streams that enter a vast sea or flow from a mighty mountain. It is vast and hence does not need to destroy any other religion for its existence. It simply absorbs and modifies them, bringing out their true spirit from their outer shell of customs and traditions. It gives an enormous freedom to discover and tune to the mighty Law of Life that holds everything in its place as part of a large cosmic order and lets them each unfold according to its own unique law. It is to this mighty Law, supreme over all man-made rules and regulations, religious and social injunctions, that the word Dharma applies. Dharma is not something imposed from outside. It is inbuilt within the fabric of our existence itself. It means that there is a Divine Wisdom and Will, a Divine Knowledge and Power that is hidden behind life. This Knowledge and Power do not act as a standard rule book of life, but on the basis of an infinite freedom and plasticity and takes into account all the different stages and types of creatures and their different natures. Hence, Sanatana Dharma cannot be reduced to a set of rules, regulations, customs and traditions that all must follow. It allows for great variety and diversity, taking into account the variations and differences in natures. Yet there are some fundamental truths (not formulas to be believed) that distinguish Sanatana Dharma. These are as follows.
There is one supreme Reality that is called by many names and can be approached in countless ways.
This supreme Reality is an infinite Existence, infinite Consciousness, infinite Force, infinite Bliss, Sacchidananda.
In terms of Space and Time and the Cosmos, this supreme Reality manifests as an Omnipresent, Omniscient, Omnipotent Truth that is also supreme Harmony and Delight. However, for the purposes of its cosmic workings, It manifests as various representative cosmic powers known as the various gods and goddesses.
There are also inverse powers or shadows of the gods, the Titans and Asuras that oppose and resist the working of the gods.
This supreme Reality is present in each element of creation. The whole creation is held within it. It has become all things as well as transcends all things.
Man can discover and even become one with this Reality through Yoga.
The soul of man evolves across a number of lives through the Law of Karma, which is the law of evolution through right choices or of self-destruction through wrong choices. This is the only relative freedom given to man, to align with the Divine Purpose in creation and within him and thereby evolve along the lines of his inner Dharma or else follow his vain desires and refuse to evolve due to inertia and weakness and thereby suffer.
This, in brief, is the Sanatana Dharma. Of course, the subject is vast and only a very brief summary is given here.
Affectionately
Alok Da
