The differences between the scriptural books of Christianity reflect a very significant fact about this religion which we need to discuss.
Christianity is named after Jesus Christ and is attributed to him, but it is not defined only by his words and acts, which are reported in the four Gospels. A number of unknown authors of its holy books have defined this religion. The apostle Paul has played a particularly influential role in this definition.
The collection of Christianity’s holy books — the New Testament — contains another 23 books written by a number of different authors, although they are said to have been guided spiritually when writing those books. The Book of Acts is attributed to the same author of one of the Gospels, Luke. A number of other authors are responsible for 9 books: Hebrews, James, First Peter, Second Peter, First John, Second John, Third John, Jude, and Revelation.
The remaining 13, particularly influential, books are attributed to the apostle Paul, as each starts with his name. But only 7 letters of these epistles, modern scholars agree, were written by Paul: Romans, Philippians, Galatians, Philemon, First Corinthians, Second Corinthians, and First Thessalonians. The latter is regarded as the earliest book of the New Testament and is dated to around 50 CE. Of the remaining six letters — Ephesians, Colossians, Second Thessalonians, First Timothy, Second Timothy, and Titus — some are subject to scholarly disagreement while others have almost all agreed were not written by Paul. Nevertheless, this modern classification of these 13 letters is almost irrelevant to the history of Christianity. For many centuries all letters were promoted by the Church as authentic Pauline epistles and have therefore played a substantial role in defining Christian theology.
The credibility of these 27 books, and ultimately the religion they represent, depends very much on the credibility of their authors. Yet the identities of most of these authors are completely unknown and their histories cannot be traced. The same argument can also be made about Judaism, whose scriptures consist of writings by various authors of whom very little if anything is known. Christianity accepts the Old Testament books also as holy scripture, so these also can be considered as sources of this religion. But Christian theologians have restricted the role of the Jewish books to providing support to the theology propagated by the New Testament books.
This is a fundamental difference between Islam and Christianity and Judaism. The credibility of the Islamic faith rests solely on the credibility of the Qur’an and the prophethood of Muhammad. Muhammad claimed to have received the Qur’an from God and that neither he nor anyone else contributed to it. The Qur’an is the only divine text in Islam. No spiritual experience of any other Muslim figure, ancient or modern, constitutes part of the faith, and no other writings have a claim to inerrability. This applies even to the words attributed to Muhammad, known as aḥādīth, or the special group of sayings known as aḥādīth qudsiyyah or “divine sayings” that are believed to represent divine revelation expressed in Muhammad’s words. These were reported down the centuries by numerous people. The fact that Muhammad’s prophethood is the only foundation of Islam is manifested in the fact that the following two verses from the declaration of faith in Islam: “There is no god save Allah” (37.35, 47.19) and “Muhammad is the messenger of Allah” (48.29).
Western scholars have questioned whether the Qur’an we have today is the same Qur’an that Muhammad taught and they have suggested that the process of compiling it was far from perfect. But even this extreme claim, which is challenged by many, is completely different from the criticism above of the New Testament and the Old Testament. Whether any ancient holy book was compiled, copied, and disseminated faithfully or not is a question that can be asked about any book. The point I make above is that Islam is based on one book that is attributed to God and one man who claimed to be God’s Prophet, whereas Christianity and Judaism are each based on a large number of books by different, unknown authors each of whom is presumed to have been guided by God.
I have ignored in the discussion of this section how Christians came to believe in their holy books or the “canon.” The reality is that early Christian groups and theologians differed on which books were holy. Actually, the earliest Christian mention that the New Testament consists of the 27 books that we have today is as late as 367 CE. It is in a letter from Athanasius, the bishop of Alexandria, to the Egyptian churches. I have discussed the question of the authenticity of the canon versus apocrypha elsewhere (Fatoohi, 2007: 23-28).