The birth of each religion is connected to a spiritual experience or realisation of some great being. Such beings have always been present throughout human history; they discovered the Eternal Reality behind creation through their intense tapasya and gave it to man as a path to be followed so that others may make the same discovery. Those who could not make the needed effort were given the principles or truths based on these discoveries to conduct our life. The former became the yoga, the latter became metaphysical philosophy and the law.
In India this Eternal Truth is referred to as Sanatana Dharma. While the yoga was mostly lost in other places it was kept alive in India, mostly through the living yogis who kept the truth alive and transmitted it to others. Many Books, many Masters, many Paths have given rise to an extremely rich, many-sided and catholic approach to the Higher/ Highest Reality thereby making the Sanatana Dharma universal in its appeal and approach to Truth and Its vast and subtle and plastic application in life.
This is the great difference between the Hindu approach, almost inbuilt in the Hindu DNA, and major world religions where things began and ended with one founder and one book. That is why it is sometimes difficult to say what is Hinduism and what is not Hinduism because much more than outer rules and regulations that are mutable and subject to change, it is this inner attitude and approach that marks a Hindu identity.
There is always a tendency in man to reduce the highest spiritual self-culture to the kitchen and the cooking pot. It is like reducing the majestic Himalayas to a snow-clad summit or confine the mighty Ganga to a little container or a small घाट (ghat) through which it flows. However, in the Hindu way of life, there is the natural corrective of admitting fresh revelations and accepting the word of realised Masters above the Scripture and the Law. This allowed not only fresh streams of spiritual experiences to flow into the human soul but also gave room to new possibilities of life making the Eternal Religion, Sanatana Dharma, at once the most ancient of all as well as the most contemporary and forward-looking.
There are and will always be people who cannot comprehend this vastness and profundity just as there are many who misuse this wideness to bring in elements that completely oppose the Eternal Law and its workings for the forward march of humanity. Well, Hinduism accepts them too with understanding and inherent tolerance until they start becoming a threat and a menace to others and above all for the manifestation of the Divine through the individual and the collective life, Nara Narayana, who are two aspects of One Reality. For the work given to it is not only to preserve the divinity in things, not only to bring out and manifest new elements of divinity in form and colour and scope and significance but also to destroy whatever has become otiose and stands now in the way to the collective forward march, lokasangrahartha, of the human race and the earth. It regards the god of creation, preservation and destruction as three faces of One Deity with the thread of dharma that connects them to each other and to the whole creation.