Why doesn't the Quran directly say that it is vague for the purpose of testing you and for you to figure out why it is vague and why doesn't it tell you that allah won't give you 100% proof because that violates the purpose of the test?
Why didn't the Quran directly state that its vagueness is because Allah wanted to test people?
First of all it did, see my article: Why is the Quran vague
But this question is a moot point, and I will explain why: it could've not mentioned it because Allah wanted us to figure that out on our own. Figure out a necessary conclusion from what it means to test humans. This too itself is a type of vagueness of the Quran--not tell you exactly why the Quran is vague: so you figure it out. Example: We could imagine be an IQ test that does not have instructions. Why not? Didn't they think there should've been instructions? Didn't they think it was important to include the instructions? Do they want the shape that doesn't fit or that fits, or either depending on the circumstance (perhaps all the other answer choices could fit the pattern and you're sometimes supposed to select the one that doesn't fit--even though the average questions asks you to select which answer choice fits the pattern--this is testing a higher level of intelligence). Why did the IQ test not mention the instructions? Did they think it wasn't important to tell you the instructions? Because part of the IQ test is to figure out what you are supposed to do--its testing IQ, after all...
First of all it did, see my article: Why is the Quran vague
But this question is a moot point, and I will explain why: it could've not mentioned it because Allah wanted us to figure that out on our own. Figure out a necessary conclusion from what it means to test humans. This too itself is a type of vagueness of the Quran--not tell you exactly why the Quran is vague: so you figure it out. Example: We could imagine be an IQ test that does not have instructions. Why not? Didn't they think there should've been instructions? Didn't they think it was important to include the instructions? Do they want the shape that doesn't fit or that fits, or either depending on the circumstance (perhaps all the other answer choices could fit the pattern and you're sometimes supposed to select the one that doesn't fit--even though the average questions asks you to select which answer choice fits the pattern--this is testing a higher level of intelligence). Why did the IQ test not mention the instructions? Did they think it wasn't important to tell you the instructions? Because part of the IQ test is to figure out what you are supposed to do--its testing IQ, after all...
Take the above example. Let's say they did not put any instructions because you are supposed to figure out the instructions. Is this a flaw or is this a feature of the IQ test? Apply the same thing to the Quran.
Now the Quran says that it is explained in detail [e.g Quran 7:52]. And this remains true, the Quran is explained in detail so much so that Allah even explained to us in [Quran 3:7] that there is deliberate vagueness and that our purpose of life is to be tested which leads to necessary inferences/conclusions as I have talked about in other articles on this site. That is an example of how the Quran is explained in detail--that detail includes that there are verses which are deliberately vague. Moreover, the Quran remains explained in detail because it leads to necessary inferences (like for example: what life being a test entails) such as that it must be sufficiently vague yet compelling to different people and such that it must support 7th century belief and modern belief. Those are necessary inferences that are derived from the Quranic verses as I had talked about on this site previously. This is a mechanism that the Quran is explained in detail: verses are given to us and those verses lead necessarily to specific inferences/conclusions when we give thought. It is explained to us in the Quran that we must give thought and reason and that Allah hates those who do not use reason to arrive at religious conclusions [Quran 8:22]. If verses in the Quran have necessary inferences/conclusions and we are told to use reason to reflect upon the Quran, then that is a mechanism of how the Quran is explained to us in detail: that there is deliberate vagueness in it, that we must use reason and reflect to reach our conclusions, that some verses have meanings that only Allah knows (again see 3:7) and that it is a test for us. How is the Quran not explained to us in detail?
Now the Quran says that it is explained in detail [e.g Quran 7:52]. And this remains true, the Quran is explained in detail so much so that Allah even explained to us in [Quran 3:7] that there is deliberate vagueness and that our purpose of life is to be tested which leads to necessary inferences/conclusions as I have talked about in other articles on this site. That is an example of how the Quran is explained in detail--that detail includes that there are verses which are deliberately vague. Moreover, the Quran remains explained in detail because it leads to necessary inferences (like for example: what life being a test entails) such as that it must be sufficiently vague yet compelling to different people and such that it must support 7th century belief and modern belief. Those are necessary inferences that are derived from the Quranic verses as I had talked about on this site previously. This is a mechanism that the Quran is explained in detail: verses are given to us and those verses lead necessarily to specific inferences/conclusions when we give thought. It is explained to us in the Quran that we must give thought and reason and that Allah hates those who do not use reason to arrive at religious conclusions [Quran 8:22]. If verses in the Quran have necessary inferences/conclusions and we are told to use reason to reflect upon the Quran, then that is a mechanism of how the Quran is explained to us in detail: that there is deliberate vagueness in it, that we must use reason and reflect to reach our conclusions, that some verses have meanings that only Allah knows (again see 3:7) and that it is a test for us. How is the Quran not explained to us in detail?