At the beginning of the 20th century many of the Lutheran parishes started to celebrate their anniversaries. Many of these parishes were older than 100 years at that time. So the anniversary always was a good occation to riffle through the church files to collect information about the church's history.
Usually it was the Pastor or a teacher who collected and published the information as a small booklet or as an article in one of the periodicals of the area.
These anniversary documents are a valuable source for historic or genealogical research. They are contemporary reports of the time of the anniversary, they give insight into historic parish details - like name lists of Kantors, teachers or members of the parish council - and they sometimes mention facts and sources which might lead the way to more detailed research.