The scholars of divinity and the writers on the history of religion usually discuss their subject under the heading of religions. For example, they talk of Prophet Ibrahim's religion, the Jewish religion, the Christian religion and the religion of Islam. They regard every Prophet to whom a code of law was revealed as the founder of a separate religion.
But the Holy Qur'an has its own terminology and its own style. From its point of view there has been only one Divine religion from the beginning to the end. All Prophets irrespective of the fact whether they had or had not an independent code of law, had the same mission and preached the same message. Their basic principles called religion were the same. Their teachings differed only in rules and subsidiary matters of secondary importance which varied according to the requirements of the time, the peculiarities of the environment and the characteristics of the people whom these Prophets addressed. But in spite of the difference in the form of their teachings, all Prophets visualized one single goal.
Apart from the difference of form there was a difference of level also. The Prophets who came later, their teachings were of a higher level in keeping with the stage of the human development. For example, there is a vast difference in the level of the teachings of Islam and those of the earlier Prophets in respect of the genesis of man, the Hereafter and the conception of the world. In other words man vis-a-vis the teachings of the Prophets is like a student who is brought up step by step from class I to the highest class. This process signifies the development of religion, not the difference of religions.
The Holy Qur'an has nowhere here used the word religion in a plural form. From the point of view of the Holy Qur'an what has existed is the religion, not the religions. There exists one big difference between the Prophets and the great philosophers and other outstanding social leaders. Each eminent philosopher has had his own school. That is why so many schools of philosophy have always existed in the world. In contrast, the Prophets have always corroborated and never contradicted each other. Had any one of the Prophets lived in the time and environment of another Prophet, he would have preached the rules of law and conduct similar to those preached by the latter.
The Holy Qur'an declares expressly that all Prophets form one single series. The earlier Prophets foretold about the later ones, and the latter Prophets acknowledged the earlier ones. The Holy Qur'a'n also says that Allah made a covenant with the Prophets to the effect that they would believe in each other and help each other. It says:
"When Allah made the covenant with the Prophets, He said. 'Here are the Scripture and the wisdom which I have given you. Later a Prophet will come to you confirming what you possess. You shall believe in Him and you shall help him. He then said: 'Do you agree to this and take the responsibility I placed on you?' They answered: 'We agree. He said: 'Then bear witness and I will bear witness with you." (Surah Ale Imran, 3:81)
The Holy Qur’an calls the Divine religion Islam and described it as a continuous process from Adam to the last Prophet. This does not mean that the Divine religion has always been known by this name. What is meant is that Islam is the best word to describe the nature of this religion. That is why the Holy Qur'an says: "There is no doubt that the only true faith in Allah's sight is Islam." (Surah Ale Imran, 3:19)
At another place the Holy Qur'an says: "Ibrahim was neither a Jew nor a Christian. He was upright in faith and a Muslim" (Surah Ale Imran, 3:67)