Religions flow inside each other. This phenomenon, which belongs to the meta-theory of religions, results from the size of the impacted group. Indeed if the religion just is a sect its teaching can be revolutionary but if the latter wants to spread over a bigger set of population, it must necessarily adapt to the pre-existential substrate of the considered religion in order to be evolutionary. In the West we all know what the Judaeo-Christian religion owes to the pagan beliefs. Nevertheless the phenomenon is completely similar in the East concerning Buddhism.
Indeed although Buddha's teaching is initially revolutionary by being distinct from the Brahmanical erudites and from the renunciates, Buddhism relies on two pre-Buddhist Indian beliefs. The first claims that all living beings returns after death and go through an indefinite series of existences among men, gods, animals and the damned. The second maintains that at each rebirth, one's share of happiness or misfortune is determined by the moral value of the acts carried out in the preceding lives according to an immanent, automatic and inescapable justice. Both these principles form the pre-existential substrate of Buddhism and it is them that allowed it to be part of the religious Indian tradition.
Despite this flow of religions we must not lose sight of the importance of the phase change which is achieved by the singular being that transforms this flow in an irreversible way. Thus the introduction, not of enlightenment since it pre-exists Siddhârtha, but of the four noble truths is a real spiritual revolution. Discovered by the Buddha, they thus say: 1) Every form of existence is by nature painful and disappointing despite the moments of happiness. 2) The origin of suffering is the erroneous vision of things that leads to avidity. 3) The end of this avidity leads to Enlightenment. 4) Enlightenment can be attained by developing ethics, concentration and wisdom. Thus Buddhism moves between two truths, relative and absolute, the conscience continuum "travels" from one life to the next pushed by the "moral" force of acts. There is no notion of immortal soul or creator God. The acute awareness of the fundamental role of suffering within existence leads to the search of a heuristics. This one by highlighting the problem of the vision leads to a new hermeneutics of the world, which results in Enlightenment. At last the Buddha shows the way because he makes clear what must be developed to attain to this transcendent state.
Nevertheless the evolution of religion does not end with this phase change. Through its own extension it diversifies and evolves into different branches, which can sometimes be contradictory with the initial impact. Thus Buddhist tantrism, which is a set of school born from mahâyâna and different from one another by their doctrines and religious practices, is distinct from Buddhism by ritual activities in which symbolism and magic play determining roles.
Through the Buddhist paradigm we see that the flow of religions is built even if it changes direction. The phase changes doesn't break this continuity even if they considerably modify its nature. In a way religions obey the first pre-Buddhist rule and do not stop transforming, as if to better explore the polymorphism of ethics.