Assalamu 3alykum brothers and sisters
Thank you Munir for your input it was nice to read your response.
To understand the verses in question we must look at them from the eyes of the people who were receiving them in the time of the prophet Muhammad(pbuh).
It's clear from the Quran that the Scripture was not sent to the Arabs all at once. It was NOT brought to them as a complete scripture in one shot.
25:32 And those who disbelieve say: Why is the Qur'an not revealed unto him all at once? (It is revealed) thus that We may strengthen thy heart therewith; and We have arranged it in right order.17:106 And (it is) a Qur'an that We have divided, that thou mayst recite it unto mankind at intervals, and We have revealed it by (successive) revelation.Taking this in consideration and putting yourself in the time the Quran was being revealed it's seems quite possible that since the people were accusing the prophet of forging the chapters he was narrating and also doubting they are from God, then it makes complete sense that God is challenging them to produce a chapter like the one being revealed if they were telling the truth. But they could never of done so because only God knows what the completion of the Quran is going to be and the whole interpretation of the verses that were already revealed to them.
So what was basically being told to them in my humble opinion and from what I understand brother Joseph is saying is that God was asking them to go ahead and complete the rest of the Quran so to speak or produce a surah or ten surahs like the ones they already received. But they could not produce it/them because they could not make it a complete sealed revelation that would answer and interpret what was already revealed to them.
So this challenge seems to only be applicable to those living in the same time as the prophet.
Regarding brother Munirs comment on verse 3:7.
And it is also said, that everyone will not understand some verses except those who are firmly grounded in knowledge (3:7).
The verse does not state that those firmly grounded in knowledge will understand all the verses or the Mutashabih verses. Quite the opposite. The best reading of this verse would be to have a break in the verse where God says, ..."none knows its explanation(full comprehension) except God. And those who are firmly grounded in knowledge say: we believe therein, the whole is from our Lord...."
This way it would be kinda problematic if read otherwise.
What the verse is stating is that no one knows the Qurans full interpretation except God.
Those firmly grounded with knowledge believe that only God knows its full interpretation and they steer away from interpreting the 'mutashabiha' (unclear) verses.
God has made it clear in that verse that those who have a ailment in the hearts who pursue the unclear verses. So the verse makes it clear that one should steer away from trying to pursue those that are unclear. That one does not try to interpret verses that knowledge of them has not reached us. Some will also remain known only to the Creator of the Universe.
We should read them same as we read all of the rest but we have to be content that there full encompassing knowledge will not be known to us. One example would possibly be verses that illustrate the Day of Judgement. We ready them with our worldly view but to understand them and interpret them to make a bigger picture than what is already told would go against the verse.
Another example which might come to pass to the people who witness that day would be verses about Gog and Magog. As you might already know the verses detail them as intended. But go to many Islamic scholars and they will tell you many stories about them that are not detailed in the Quran. Have they crossed the boundaries of this verse?
Also you are correct there is two types of verses in the Quran. Muhkam and Mutashabih. The Quran makes it clear in the same verse that the foundation, mother, or majority of the Quran are clear and understanding to the readers/community to derive laws and rulings and use as a complete guide. The rest would be unclear.
Those who are firmly grounded in knowledge believe all of the Quran is from God whether they comprehend the full knowledge or not they believe in the entirety of it.
You also said
With the advance of time knowledge advances and the meaning of mutashabih verses becomes more clear, or we can say, we get different ways to understand the meaning of the verses. So, understanding Quran is a a continuous process. And this could be a miracle. Because no other book is like this type.
I agree. This may be possible. It's clear that there is verses in the Quran that illustrate a period that will come to humans that is called the Hour. The Quran speaks about this in many different ways. It could be argued that when the time comes to pass the verses would become more clear but also arguably too late for anyone to believe as well.
Hope that helps Insha'Allah
Salam