DODSON, Mont.—People don't grow into mature Christians until they serve others. So says American Indian pastor and ministry leader Bruce Plummer, of Sioux, Assiniboine, and Cree heritage.

In his multifaceted ministry, Plummer invites mission teams to come to Montana to serve with Montana Indian Ministries: picking up trash and handing out water and coffee in four weeks of powwow ministry, five weeks of Indian camp ministry for children and youth, and construction/maintenance/mercy ministry to people on the reservation.

Plummer also takes mission teams from four Montana reservations to do...