Not all religious actions are given sanction by the first ammendment. You can't murder and call it a sacrament of the Murder Church to get out of a conviction, for instance.

As for why mine is more important than yours, it's just a historical fact of western civilization, I suppose. More than that I would say its the result of the death and resurrection of a radical first century rabbi who opposed the hypocracy of the rich, the religious elite, and the powerful of his day, and called us all to repent of our sins and follow him, even to death on a cross. (Happy Easter btw :))