I was explaining Islam to a non-Muslim friend. He came up with a couple of questions that actually confused me as well. I have been told since I was a kid that Islam is one true religion and everything else is a lie. How can I be sure that it is not a man-made religion and it really is the truth? I have gone through the embryology example. Anything else that could prove the divine presence in holy Qur'ān?
In order to understand whether Islam is a man-made religion or not, one first needs to understand and appreciate what actually Islam means. Islam is the name of the religion that is embodied not only in the nature of a human being but in fact in the nature of everything in the world. Islam is therefore the religion of all the prophets of God. Islam in its conceptual meaning simply means to surrender to God and in its conventional meaning simply means a set of directives that set the person free from any other thing so that the person can surrender himself to God.
I think at least for a believer in God, the above definition of Islam, conceptual and conventional, should be acceptable.
The question then will be, how we can we make sure that the religion that the Qur'ān talks about is the same Islam that we introduced above. In other words, how we can make sure that the Qur'ān was not the work of a human being and was actually revealed by the Almighty Himself.
One way to answer this is to think what would be the other explanations (other than the belief that the Qur'ān is revealed by God). Other explanations need to be thought of only after appreciating the following facts (among many others):
1. The process of revelation of the Qur'ān extended 23 years during which the Prophet (sws) led a very adventurous and unsettled life.
2. Evident from the history and the Qur'ān itself, the style of the Qur'ān has a beauty and influential elegance that was unfounded in any Arab literature at the time. This was the reason that the "author" of the Qur'ān challenged its immediate addressees if they could produce anything like that.
3. While being a work that completed only in 23 years, there is a very solid and systematic link and correlation between the verses and their concepts throughout the Qur'ān (this I admit can only be appreciated by one who studies the Qur'ān in depth).
4. The Prophet (sws) was never known as a person who would be able to say poetic pieces or as a person of knowledge and reading. He was either almost illiterate or at least not a reader of any literary works.
5. The Prophet (sws) was a very successful and charismatic leader, in other words his life was not limited to uttering the verses of the Qur'ān.
6. The promises of the Qur'ān about the victory of Muslims and their prosperous life in this world and the perishing of their enemies came literally true despite all the apparently rational odds.
7. While the Qur'ān is inline with the previous divine scriptures, it provides some alternative explanations about the theological and historical aspects of the previous religions. These alternative explanations often sound more rational and intellectually superior than those that are offered by these scriptures or their followers.
Any one who intends to provide an explanation about the source of the Qur'ān needs to consider the above points in the process. I would like to argue that (at least for a person who believes in God and previous scriptures) the explanation that "the Qur'ān has been divinely revealed to the Prophet (sws)" matches all the above points perfectly and that no other explanation provides such a perfect match.