Spoken language predates written language. In spoken language the words are supplemented by inflection, pace, pauses, even facial and body expression. When we invent an alphabet and start writing, the words are represented by symbols, but the cadence and pace are missing. Punctuation is an attempt to emulate speech patterns. The most common punctuation marks are the period and the comma.
Periods are reasonably clear.
Not many people misuse periods, expect maybe to not use enough of them, but that's another topic. I'm done with that thought and will now go on to another. Imagine you are speaking the sentence instead of writing it. If you come to a point where you would give a word a slight inflection or emphasis and pause, you probably could use a comma. A sentence that flows without a pause doesn't need a comma.