Ministry Sieck's first call was to Emmanuel Lutheran Church in
Hamburg, Minnesota. He came to Zion Lutheran Church in St. Louis as assistant pastor in 1905, becoming pastor in 1914 following the death of pastor Charles F. Obermeyer, his father-in-law. He was involved with several Lutheran organizations, including the St. Louis Lutheran Publicity Organization and
The Lutheran Witness.
Concordia Seminary Sieck served on the Board of Control of Concordia Seminary from 1939 to 1943. In 1943, Sieck left Zion Lutheran Church to become the president of Concordia Seminary following the end of
Ludwig E. Fuerbringer's tenure. During his ten years as president, enrollment reached a record high of 840 students and several new buildings were built. He taught pastoral theology. At the time of his death, Sieck was chairman of the National Advisory Emergency Planning Council of the Evangelical Lutheran Conference. He was also vice-president of the
State Historical Society of Missouri and served on the board of
Valparaiso University. == Personal life ==