It’s God’s calendar, not just the Jewish calendar. These dates (Passover, Trumpets, Day of Atonement, Tabernacles, etc.) were given by God in the Torah (Leviticus 23) long before modern Judaism existed. They are called mo'adim — “appointed times” — and the Bible presents them as the Creator’s own sacred rhythm for all who want to walk in step with Him.
The year starts in spring and is tied to the moon + agriculture Unlike the Gregorian calendar (January–December), the biblical year begins with the month of Passover (March/April) when barley ripens in Israel. Every month starts with the new moon, and the feasts are perfectly synced with the harvest cycle — spring feasts celebrate redemption and firstfruits, fall feasts celebrate ingathering and final atonement.
Jesus (Yeshua) and the early church celebrated these exact days. The Last Supper was a Passover seder, the Holy Spirit fell at Pentecost (Shavuot), and the dramatic events Christians expect at the Second Coming (trumpets, atonement imagery, tabernacles) line up with the fall appointments. So this calendar isn’t “old Jewish tradition” — it’s the timeline God Himself gave for the entire redemption story.