There is no relation between words and the things they represent. Still less then, are there necessary signs for abstract and highly variable concepts. There are an infinite number of possible sentences. We speak the way we speak today because of series of historical accidents and contingencies . Each community speaks a different dialect, and people speak many different dialects depending on the social situation.
Spoken language is different from writing.
Speech and writing involve different parts of the brain. For most of linguistic history, we know only the history of written language. Spoken language predates written language historically. Written language is much more stable than spoken, especially in societies that have technologies of printing but have not yet developed technologies of mass aural media. So our written language became standardized quickly after the introduction of printing into Britain after 1470.