The following is an exceprt from the Introduction to the Bhagavad-gita As It Is by HIs Divine Grace A.C.Bhaktivedanta Swami Prabhupada, the founder and spiritual master of the Hare Krishna movement, where he explains the true meaning of the world "religion" and how we misunderstand it to be a mere faith.
The Supreme Lord and His transcendental abode are both sanatana, as are the living entities, and the combined association of the Supreme Lord and the living entities in the sanatana abode is the perfection of human life. The Lord is very kind to the living entities because they are His sons. Lord Krsna declares in Bhagavad-gita, "sarva-yonisu...aham bija-pradah pita." "I am the father of all." Of course there are all types of living entities according to their various karmas, but here the Lord claims that He is the father of all of them. Therefore the Lord descends to reclaim all of these fallen, conditioned souls to call them back to the sanatana eternal sky so that the sanatana living entities may regain their eternal sanatana positions in eternal association with the Lord. The Lord comes Himself in different incarnations, or He sends His confidential servants as sons or His associates or acaryas to reclaim the conditioned souls.
Therefore, sanatana-dharma does not refer to any sectarian process of religion. It is the eternal function of the eternal living entities in relationship with the eternal Supreme Lord. Sanatana-dharma refers, as stated previously, to the eternal occupation of the living entity. Ramanujacarya has explained the word sanatana as "that which has neither beginning nor end," so when we speak of sanatana-dharma, we must take it for granted on the authority of Sri Ramanujacarya that it has neither beginning nor end.
The English word "religion" is a little different from sanatana-dharma. Religion conveys the idea of faith, and faith may change. One may have faith in a particular process, and he may change this faith and adopt another, but sanatana-dharma refers to that activity which cannot be changed. For instance, liquidity cannot be taken from water, nor can heat be taken from fire. Similarly, the eternal function of the eternal living entity cannot be taken from the living entity. Sanatana-dharma is eternally integral with the living entity. When we speak of sanatana-dharma, therefore, we must take it for granted on the authority of Sri Ramanujacarya that it has neither beginning nor end. That which has neither end nor beginning must not be sectarian, for it cannot be limited by any boundaries. Yet those belonging to some sectarian faith will wrongly consider that sanatana-dharma is also sectarian, but if we go deeply into the matter and consider it in the light of modern science, it is possible for us to see that sanatana-dharma is the business of all the people of the world -- nay, of all the living entities of the universe.
Non-sanatana religious faith may have some beginning in the annals of human history, but there is no beginning to the history of sanatana-dharma because it remains eternally with the living entities. Insofar as the living entities are concerned, the authoritative sastras state that the living entity has neither birth nor death. In the Gita it is stated that the living entity is never born, and he never dies. He is eternal and indestructible, and he continues to live after the destruction of his temporary material body. In reference to the concept of sanatana-dharma, we must try to understand the concept of religion from the Sanskrit root meaning of the word. Dharma refers to that which is constantly existing with the particular object. We conclude that there is heat and light along with the fire; without heat and light, there is no meaning to the word fire. Similarly, we must discover the essential part of the living being, that part which is his constant companion. That constant companion is his eternal quality, and that eternal quality is his eternal religion.
When Sanatana Gosvami asked Sri Caitanya Mahaprabhu about the svarupa of every living being, the Lord replied that the svarupa or constitutional position of the living being is the rendering of service to the Supreme Personality of Godhead. If we analyze this statement of Lord Caitanya, we can easily see that every living being is constantly engaged in rendering service to another living being. A living being serves other living beings in two capacities. By doing so, the living entity enjoys life. The lower animals serve human beings as servants serve their master. A serves B master, B serves C master and C serves D master and so on. Under these circumstances, we can see that one friend serves another friend, the mother serves the son, the wife serves the husband, the husband serves the wife and so on. If we go on searching in this spirit, it will be seen that there is no exception in the society of living beings to the activity of service. The politician presents his manifesto for the public to convince them of his capacity for service. The voters therefore give the politician their valuable votes, thinking that he will render valuable service to society. The shopkeeper serves the customer, and the artisan serves the capitalist. The capitalist serves the family, and the family serves the state in the terms of the eternal capacity of the eternal living being. In this way we can see that no living being is exempt from rendering service to other living beings, and therefore we can safely conclude that service is the constant companion of the living being and that the rendering of service is the eternal religion of the living being.
Yet man professes to belong to a particular type of faith with reference to particular time and circumstance and thus claims to be a Hindu, Muslim, Christian, Buddhist or any other sect. Such designations are non-sanatana-dharma. A Hindu may change his faith to become a Muslim, or a Muslim may change his faith to become a Hindu, or a Christian may change his faith and so on. But in all circumstances the change of religious faith does not effect the eternal occupation of rendering service to others. The Hindu, Muslim or Christian in all circumstances is servant of someone. Thus, to profess a particular type of sect is not to profess one's sanatana-dharma. The rendering of service is sanatana-dharma.
Factually we are related to the Supreme Lord in service. The Supreme Lord is the supreme enjoyer, and we living entities are His servitors. We are created for His enjoyment, and if we participate in that eternal enjoyment with the Supreme Personality of Godhead, we become happy. We cannot become happy otherwise. It is not possible to be happy independantly, just as no one part of the body can be happy without cooperating with the stomach. It is not possible for the living entity to be happy without rendering transcendental loving service unto the Supreme Lord.
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