First of all, why is there a Book of Songs? The rulers of the Zhou dynasty sent a lot of manpower and material resources to collect these poems among the people and compile a book to educate the king, who then used it to educate the people. Why? Is it to inspect the folk customs? Although there are reasons for this, communication is more important. Kings can quote sentences from the Book of Songs when negotiating with each other. As the world gets smaller and smaller, kings and ministers, central and local governments need to ensure communication. Therefore, The Book of Songs is the earliest mandarin.
The Qin dynasty unified the world, why write the same book? Or for the sake of smooth government orders. The change of seal script to official script is nothing more than for the convenience of writing. The font has changed, and the dialect language has changed because of the war, but the central government must have a set of communication methods between bureaucrats, perhaps Xi' an dialect? Just like our Mandarin now.
The need of government decrees, especially the opening of the imperial examination in the Tang Dynasty, made poetry writing a skill of promotion and wealth, and poetry flourished. In addition, with the development of phonology and the appearance of rhyme books, every word has a rhyme. What's so hard to read?
Chinese character, a square character, is a very stubborn combination of sound, meaning and form. It's hard to learn, but it's tenacious, which also ensures that China culture is never out of date. Even the history has been recorded by historians, so it is not difficult to record the sound changes of some words. Therefore, as long as you are willing to study and look through the previous rhyme books, you will naturally find those changed pronunciations, not to mention that although many words have changed, more words have not changed under the protection of Putonghua. Since most of them have not changed, today's pronunciation must still rhyme. Even if it doesn't rhyme, you can find the original pronunciation from ancient books, such as "oblique" reading "summer"
Remember that poetry rhymes. If a poem doesn't rhyme, it must be that the pronunciation of rhyming words has changed. As long as you look up Pingshui rhyme or even earlier rhyme books, you will definitely find the correct pronunciation.
It's like we haven't learned traditional Chinese characters, but if you look at them, you will recognize almost all of them. The culture in the blood can't be cut off so easily.
The only thing that may lead to this incomprehensible situation is that during the Republic of China, some people proposed to completely latinize Chinese characters. If we had been educated in Latin since childhood, just like those children living abroad now, we would have no knowledge of Chinese at all, let alone the pronunciation of words in China's history. It is not the change of words and sounds, but that they have no concept of Chinese characters at all.