The foundation of Allah's (ﷻ) Book is literal, as mentioned in the Qur'an itself. This is true of most of its verses. And they have been explained in detail by the Prophet (ﷺ), so there is no confusion. So when you ask, "the real ruling is in the Quran" - it is explained via the Sunnah. That is not hidden knowledge.
In addition to the literal verses, there are also some parables in the Qur'an. (Yes, the verse you referenced is speaking about parables). ►The wisdom behind parables is to make people contemplate and use their brains more deeply, as well as Him using them to guide/misguide with.
"Indeed, Allah is not timid to present an example - that of a mosquito or what is smaller than it. And those who have believed know that it is the truth from their Lord. But as for those who disbelieve, they say, "What did Allah intend by this as an example?" He misleads many thereby and guides many thereby. And He misleads not except the defiantly disobedient ~ Qur'an 2:26.
The Qur'an is described as the "Furqan" (criterion, ie distinguishes between truth and falsehood). Likewise, it distinguishes between the Believers and Disbelievers. The Believers read it and believe in it (and it heals their hearts). In contrast, the Unbelievers read it and question it/quarrel (and it increases them in anguish).
All of its verses are the truth from Allah (ﷻ). Easy to read/memorize/learn.