Christians benefit from a closer look at the Biblical Fall Feasts, because, among other things, they foreshadow Christ's work in days to come. We have hindsight to help us see how Christ fulfilled Passover, Unleavened Bread, First Fruits, and Pentecost. We need foresight to see how he will fulfil Trumpets, Atonement, and Shelters.
This helps us understand why there are two New Years in the Jewish calendar: the religious-year cycle of teaching starts with Trumpets, but the calendar-year starts just before Passover. Some people start their spiritual lives at the beginning with Creation and the Old Testament (Jewish), but some start with Jesus the Passover lamb (Christians).
The religious annual cycle begins with Creation, the First era:
Whether you start with Creation, or start with Christ, the Feasts commemorate the whole of history, from the very beginning to the very end of the age.