"In the same way, monks, those things that I have known with direct knowledge but have not taught are far more numerous [than what I have taught]. And why haven't I taught them? Because they are not connected with the goal, do not relate to the rudiments of the holy life, and do not lead to disenchantment, to dispassion, to cessation, to calm, to direct knowledge, to self-awakening, to Unbinding. That is why I have not taught them.
This is quite easy to understand, but always language will fail us on one level. When one does formal meditation, or sutta study there is only the meditator and the one who is reading. Inside of the process or experience there will be so many micro level experiences that only the reader of the sutta and the meditator will experience for themself. We all have unique conditions, not any two of us are the same experience, we all have unique features, experiences and perceptions. We cant actually share and discuss those micro experiences as they they are far to subtle, to try and mold everything into one experience and doctrinal understanding is not wise, but yet underneath it all there is a certain objectivity, a common shared experience.
A simple example for reflection is if one eats an apple, can we really describe exactly the taste and the experience, we could comment on the some of the universally accepted facts, an apple is green and red, inside are pips, its often either sweet or slightly bitter. But then other apples maybe just red, or just green, some with more sweetness or some more bitter, so there is really no shape or taste to an apple. Some may not like apples, if someone has never seen an apple they might not think it exists until they eat it. But somehow we have developed through language and experience a way to talk about apples and we all know what an apples is. no need to go into all the micro details, just eat it mindfully, and experience, no need for any outside verification from anyone, if others dont like or cant understand, will it stop another person from eating apples.
Another example is a colour, a simple objective colour that we see everyday like red. Try and explain that colour to a blind person, how can you do it, but if one has sight ts easy to see red, to study red, to work with red, to fit into designs, the colour red is unlimited in how it can be used and applied within the colour schemes of life. So may things within experience are just apparant here and now but explaining all the micro details and every single individual experience is just impossible.
Often in text study the language is coded in a such a way that all the micro details are condensed into grammar, when codes are cracked by reflection and application then the code break opens and far more comes out than just simple compound syllables of the letters. None of that can really be explained, although its not abstract, it gets shared and understood in other forms of communication beyond ordinary appearances.
The sound of silence perhaps.