From issue 61 of Reformed Worship magazine:
How can New Testament Christians benefit from celebrating Old Testament festivals? We discovered three benefits that made these services worthwhile.
First, our congregation is better able to understand the context of God’s mighty acts. Our immersion in Old Testament ways of celebrating helped us understand a big part of our Bibles of which we were previously unaware. The much-loved rubric of “promise and fulfillment” is made richer when we celebrate the promises as God revealed them and intentionally point to their fulfillment in Christ.
Second, these services illustrated how God has provided for children throughout history and helped us focus on ways of keeping covenant with younger generations. We gained a renewed appreciation of our obligation to celebrate the high Christian holidays in child-friendly ways that teach little ones the mighty acts of God. These services have given new impetus to us as church leaders to be thinking about ways the Christian holidays, including the neglected holidays of Ascension Day and Pentecost, can be reclaimed. We have also come to see that symbols and traditions that detract from the real story of the day (such as secular symbols that encroach on Christmas and Easter) should be purged without remorse.
Most important, these services helped us worship and bring glory to God. The original festivals (and our services) were designed to show all generations God’s amazing cosmic plan to redeem creation and restore what was broken at the fall. The festivals and our worship have drawn all of us who have ears to hear and eyes to see to a renewed awareness that God loved the world, and did so with such a fierce, stubborn, and unrelenting love, that God’s only Son came into the world so that we might be saved and not condemned.