This is the month where harvesting is coming to an end. In the past, festivals were held to mark that end and other loose ends of the year were tended to--such as all rents and payments were due and it used to be when elections were held.
September is a transitional month as we go into Fall--our bodies and minds start to turn to other things--sort of a battening down the hatches and a turning inward. A time to start to "take care".