In Spring of 1934, the two accepted the Mennonite General Mission Board’s call to start a mission church in [[Hannibal, Missouri]].ref This Gospel Mission was founded in Hannibal on June 3, 1934, under the South Central Mennonite Conference, and would eventually become known as the [[Mennonite Mission Church (Hannibal, Missouri)|]]. While serving in the area for the next 22 years, their mission work received national recognition, Nelson was appointed as bishop over five congregations and as President of the Mennonite Board of Education, and Christmas Carol published several novels based on stories of those she met or stories which were submitted to her. Of particular note is the work of the Hannibal mission within several Missouri prisons, work which resulted in the conversion and baptism of Johnnie Allison, who would eventually be convicted of the murder of his father-in-law. As a result of a personal connection with Nelson and Christmas Carol Kauffman, Allison became passionately religious, and worked to convert other prisoners, even creating a Mennonite church within the [[Missouri State Penitentiary]] in [[Jefferson City]]. Johnnie Allison and Christmas Carol Kauffman would collaborate to publish the story of his conversion under the name Life with Life, although Allison's wife raised a libel lawsuit over its publication. After his release, Allison maintained a friendship with the Kauffmans, and even visited Christmas Carol while she was hospitalized in .ref
After ending their mission work in Hannibal in 1956, the Kauffmans moved to [[Elkhart, Indiana]], where Nelson served as Secretary of Home Missions for the Mennonite Mission Board and the two began attending Belmont Mennonite Church.ref Christmas Carol remained in Elkhart until her death in 1969.