Time. It’s important- mostly because of what we do with it. Or, what we don’t.
We used to tell time with sundials. Until we were able to develop sophisticated mechanical pieces that made our obsession with the time be possible, regardless of the weather. My religion uses the concept of hours- but those hours change in length as the day gets longer or shorter- since daylight is defined as containing 12 ‘hours’- and so is night-time.