Why are calendars important?

Calendars are extremely important because they give information about the changes that occur as we travel through the 365 days of the year. The Earth takes a bit longer than 365 days to travel once around the Sun and return to the exact position which it occupied relative to the Sun at the beginning of the year. That is why we add an extra day every four years. In fact even that extra days does not allow the Earth to reach its absolutely exact position, so further corrections are necessary at the ends of centuries.

Centuries ago people did not know such facts and the rulers would declare that a year would have as many days as their best astronomers could advise.

However these errors gradually multiplied to such an extent that the "Seasons" did not occur at the right calendar dates. If the seasons were out, then farming with animals and crops could not be done properly.

That is extremely important, isn't it?