Commas as Means of Readability - Writing English
Commas help to keep the structure of the sentence clear so that the text is easy to read and understand. A text is well structured if the reader knows where to pause.
Beispiel: Above, the eagle flew gracefully through the air.
Note: Without the comma, the sentence might be confusing for the reader as the first three words can be seen as a unit (“Above the eagle …”). Of course, the sentence does not work this way, but the reader might have to read the sentence again to get the message. Using a comma after “above”, the author makes the sentence easier to read and understand.