The substance of capitalization and punctuation is this: you must be able to comprehend what the speaker is saying; that is, when it has written on paper.
Envision if I were to say that sentence again, but this time, devoid of all the punctuations and capitalizations. It would be extremely confusing, and very hard to understand.
Otherwise, look at it this way: Pretend you are reading the Bible. Without punctuation and capitalization, the Bible would sound a lot like a bunch of nonsense. God’s name would sound like just a simple word with no real significance. It would be extremely aggravating, and bewildering.
In addition, what if people would just randomly come up to you and start speaking without pauses in their speeches. Imagine your parents telling you something important, but their words were together without a pause.
It could be really, really irritating, or you could mishear and do something you weren’t supposed to do.