The Jewish calendar is based on a lunar model with an added month every 7 out of 19 years. This is done so that is will be synchronized with the solar year. Here is a look at their calendar. September is the start of the Jewish Year. Along with Passover, on the first 2 nights is the Seder service which tells the story of Exodus.
Calendars are a very important part of a person's culture or religion.
It tells what is important to them.