6 to Consider, by Sharif Abu Laith

1. The Quran is understood to be the speech of God revealed over a 23 year period to Prophet Muhammad ﷺ.

2. The Quran is considered a perfect composition of Arabic language such that it is impossible for humans to imitate it.
The first reason is that it is perfect, in that it's free from any grammatical mistakes & syntactical errors, and free from internal or external contradictions.
That doesn't necessarily sound anything special but it should be known that when the verses of Qur'an were revealed, they were revealed in parts, not altogether as one book. Some of the verses were revealed to address specific evil events during the lifetime of the Prophet ﷺ.
So the Prophet would be asked a question or accused of something so the verses were revealed to, and then repeated by, the Prophet ﷺ in various circumstances -- without there being a possibility of editing what was recited-- yet it was considered perfect in its composition, with no errors.
For example, in the way we speak, we make grammatical errors.
Whenever we write something at length. we normally need post edits.
Yet none of this was open to the Prophet ﷺ ; at once he recited it, often particularly to non-Muslims who were against Islam, and who were looking to pick out any mistakes (then, if he made a mistake it would have completely discredit his claims of having this perfect revelation).
Secondly, the Qur'an has a unique genre or style to its sound.
This was unique to the Arabs at that time. It was neither poetry, (i.e. having one of the 16 different rhythmical patterns of poetry known in Arabic poetry as al-Bihar). Nor was it prose.
But it contained a unique sound.
Thirdly, the level of meaning contained in the Quran couldn't be matched.
The Quran was able to bring together brevity, as well as beauty, in each and every verse. Such that, it was impossible to change the verses to add to the expressiveness of its meaning.
Nor did it use any superfluous words that wasn't needed.
So every single verse was considered perfect for the subject matter it came to explain. The non-Muslim Arabs as well as Muslim Arabs recognised that the Qur'an was not only unique, but also inimitable.

Here's some quotes from experts in Arabic language.

“As has been noted, the language of the Qur'an is regarded as surpassing everything that can be written in Arabic.
The Qur'an itself is a miracle and cannot be imitated by man.”
Joseph Schacht with C.E. Bosworth, 1974 p321

“That the best of Arab writers has never succeeded in producing anything equal in merit to the Qur'an itself is not surprising”
Professor E.H. Palmer in his introduction to “The Koran”, London 1820

“Well then, if the Qur'an were his own composition other men could rival it. Let them produce ten verses like it. If they could not (and it is obvious that they could not) then let them accept the Qur'an as an outstanding evidential miracle.”
H.A.R Gibb, “Mohammedanism”, London, 1953, p33

3. There's a number of other things.
Firstly, we rationally arrive at belief in a Creator.
It's rational to believe in only One God.
It's rational to believe God is not like limited dependent creatures.
So God is transcendent beyond creation.
Therefore Islam's and Muslims conception of God is in accordance to our rational conception of God.
Secondly, we all have a nature that drives us to seek out a purpose in life.
We desire to perform moral acts. And we desire to sanctify something transcendent. Those innate attributes we have pushed us to seek out further communications and a relationship with this Creator who is the ultimate foundation for creation and our own existence.
Therefore we'd seek out a message from this creator.
We hear of many claims to prophethood but any claim would need to fit within our rational conception of the creator. I.e. a singular transcendent being Who is the Creator of all creation.
Islam fits both the rational conception of God, and also satisfies human desire for meaning purpose guidance and the desire to sanctify.

Furthermore, the prophets of the past including prophet Muhammad ﷺ came with a sign that indicated they were messengers.
For prophet Muhammad ﷺ that sign was the inimitable nature of the Qur'an.
I.e. the Quran is beyond human productive capacity. Therefore, it's only rational that if humans couldn't have produced the Qur'an, then it must come from this transcendental Creator.
This is in addition to the many prophecies that have come to pass, and physical miracles performed by the Prophet ﷺ with the permission of the Creator.
Furthermore, the transformative power that Islam created within the Arabian peninsula that developed a unique civilisation.
Taken together, we have a powerful justification for Islam being true.

4. We can question Islam.
We do so to test and ensure the message is truly from God.
Whenever any questions are raised we find that Islam is robust enough to answer all these questions. Thus establishing that the revelation is from an all-knowing all-wise Creator Whom we submit to, because we have good reasons to fulfil what God wants, as He knows us better than we know ourselves and He knows what's best for us better than we do.

5. Prophet Muhammad ﷺ is a messenger of God, and this is demonstrated in his life and character.
He ﷺ is a living example to follow so that we can attain the best in this life and the next life through salvation.
In a number of verses in the Qur'an does it tell us to follow the Prophet ﷺ in matters that he ﷺ was given as revelation.
So we don't have to dress like the Prophet ﷺ, but how he ﷺ dealt with people and how he ﷺ worshipped are guides for us to implement in our lives.

6. If as humans we try to establish morality for ourselves it will end up being subjective. And people will differ as they have done throughout history. Even if we have intuitions about morality-- those intuitions were created and instilled in us by God. Therefore, if God now is rationally established, and the Qur'an is rational established as being from this all-wise all-knowing Creator then we submit our subjective moral understandings and justifications to God's ultimate understanding of what is good and bad.
- Sharif Abu Laith [edited by mdthr]