The Dhamma realized by the Buddha was unheard before.
The Buddha said in His first sermon, the Dhammacakka Sutta, that the Dhamma which He preached was unheard of before. Knowledge of the Dhamma which arose was clear to His vision, to His knowledge, to His wisdom, to His penetration, and to His Enlightenment.
Some people claim that the Buddha did not preach a new doctrine but merely reformed the old teaching which was existing in India. However, the Buddha was no mere reformer of Hinduism as some protagonists of this ancient creed make Him out to be.
The Buddha’s way of life and doctrine were substantially different from the way of life and the religious beliefs people had in India. The Buddha lived, taught and died as a non-Vedic and non-Brahmanic religious Teacher. Nowhere did the Buddha acknowledge His indebtedness to the existing religious beliefs and practices.
The Buddha considered Himself as initiating a rational religious method, as opening a new path. In fact He had revolutionized the religious way of life in a dignified manner.
That was the main reason why many other religious groups could not agree with Him. He was condemned, criticized and insulted by the most noted teachers and sects of the Vedic-Brahmanic tradition. It was with the intention of destroying or absorbing the Buddha and His Teaching, that the Brahmans of the pre-Christian era went so far as to accept the Buddha as an Avatara or incarnation of their God. Yet some others despised Him as a vasalaka, a mundaka, a samanaka, a nastika and sudra. (These words were used in India during the Buddha’s time to insult a religious man).
There is no doubt that the Buddha reformed certain customs, religious duties, rites and ethics and ways of living. The greatness of His character was like a pin-point that pricked the balloon of false beliefs and practices so that they could burst and reveal their emptiness.
But as far as the fundamental, philosophical and psychological teachings are concerned, it is groundless to say that the Buddha had copied ideas from any existing religion at that time. For instance, the idea of the Four Noble Truths, the Eightfold Path and Nibbana, were not known before His coming. Although the belief in kamma and rebirth was very common, the Buddha gave quite logical and reasonable explanations to this belief and introduced it as natural law of cause and effect. Despite all these the Buddha did not ridicule any sincere existing religious belief or practice. He appreciated the value in many where he found Truth and he even gave a better explanation of their beliefs. That is why He once said that the Truth must be respected wherever it is. However, He was never afraid to speak out against hypocrisy and falsehood.