When you start to discuss a subject, a common way to introduce it is by giving a historical background. Let's do this, then.
Many cultures have developed some sort of traditional knowledge on languages. Rhymes and verses, for instance, shows that some primitive understanding of phonetics is present.
The first (if not the first, one of the oldest and most important) systematic analysis of the speech was the alphabet. Although the alphabet doesn't tell us a lot about many linguistic features, it does denote a remarkable understanding of phonemes. (ok, I'll discuss phonemes later) In other words: you don't create a writing system just like that. You must think a bit about language and find how it works. When the ancient cultures began to write, they were forced to thought about language and they did. In some cases, it didn't go any further. In other cases it did. I'll discuss it later in another post.