Why were calendars important to the Egyptians?
they were important because to keep track of the number of days between flooding cycles.
There are no calendars centred around universalising religion. Calendars, and there are many of them, were originally created to count time. As religions became more important to mankind they included regular religious festivals and as the various priesthoods were of the few that received any form of education they became the guardians and regulators of calendars. In effect they usurped their uses and controlled them.