The way they celebrated it at our church it was called a homecoming.basically a feast/buffet style dinner(everyone would bring a dish of food to be shared ). Basically a all day church meeting ending with the dinner or in the bible it would be called the feast of tabernacle(sukkot).o r ingathering of the church body-the jews being brought into the promise land. Sort of a day of christian thanksgiving for God delivering us all out of our desert(everyday life into heaven). Then later that year we would have basically a meeting,day at a park,playing games basketball,softball,running around on the trails,just being together and having a big buffet meal together sort of a church family get together. Showing everyone you don't have to be a stuffed shirt to be a christian.now if you want a real church anniversary it would be the birth of Jesus(or as the date is celebrated as christ/mas)because without his birth there would be no anniversary of the church(the church body) to celebrate the beginning of christianity(believing in Jesus as lord and savior).so it depends on what anniversary you are talking about with the church in mind.