Long ago church leaders wanted to make sure that their teachings covered all the important stories. They devised a calendar, prescribing certain Bible passages and stories that should be taught. You can find the current church calendar here.
I have to admit that I don't know a lot about the calendar, but I do know that I need regular reminders. In the season of Lent, I need to remember my own mortality, need for the grace of God, and the great sacrificial love that Jesus gives to me.