Once one speaks of religions, they can categorize it in two: Divine religions and man-made ones.
Man-made ones: Some of the religions are not basically divine and they do not also claim to be so like primitive religions such as animism, pre-animism, totemism, fetishism, and philosophical religions like Buddhism, the religion of Confucius. The differences among religions are totally natural as these religions are basically derived from thought, culture and human history. The causes of differences are resulted from the differences of their genesis and founder.
2- Divine Religions:
The religions which God has appointed a prophet for and sent revelations to mankind fall into this category. From the viewpoint of the Holy Quran, all the prophets from Adam to Mohammad invite mankind to one school of thought. Accordingly, all the prophets follow a set of common principles and precedents like invitation to monotheism, abiding by God-wariness, annulling herolatry, seeking unity, glad tidings and warnings, tolerance of enmity and derision, invitation to the sublimity, and etc. However, the prophetic religions differ in some respects including:
1-Different communities, environments, the necessity level, people`s talent: That the prophets were sent to guide mankind is undeniable. Thus, the orders, content, teachings should be in accordance with the society`s knowledge and environmental needs. Naturally, mankind had very restricted social relations at first centuries and its social system was not extended. Hence, very limited laws controlled and governed its life. Different ideas and beliefs were yet to be surfaced in society so that it needs to warnings for reformation. The extension of mankind`s mental horizon, relations, knowledge, and occurrence of natural phenomena and necessities gradually led to the rise of new invitation, messenger-ship, and prophet, which finally paved the ground in the society for the invitation of Islam and Allah`s last invitation.
2- The occurrence of distortion:
As time passed by, some distortion and deviation came to existence by some ignorant followers, the religious leaders or contemptuous self-indulgent officials of the society in which case another prophet was required to show the deviations and purge the previous religion off its impurity or to introduce a new religion for pure divine creed.
As on the onset of Islam was synchronous with the dawn of mankind`s domination over documentation, composition, and compilation and preservation of his own works, the Holy Quran was kept intact against any kind of distortion, and most of the Noble Prophet and Imams of Guidance`s traditions, narrations and works were preserved for the successors. Henceforth, there exists no need to revive the invitation and appointment of a new prophet.