Religious practices keep important truths about God alive. When we encounter a religious practice, it is always insightful to try to figure out what truth it is keeping alive. A religious practice not assigned to a truth about God is a fetish - a superstition.
The Mass is An Echo of the Original
The Mass is an echo of the revelation that Jesus released into the Valley of Tears on the road from the Crucifixion to the Resurrection. We took from him that which did not belong to us, his life. He gave to us that which we did not deserve, forgiveness. Upon this unjust transaction between creatures and creator, the entire edifice of Christianity rests. The Mass propagates across time and space this paradigm shifting revelation about the nature of God.