As a boy, Milton was an avid reader. Despite long hours working on the family farm, he studied a wide range of subjects and prided himself on his efforts to improve himself and to train his mind to think. Drawn to a religious life as a young man, Milton joined a Midwestern Protestant sect called the Church of the United Brethren in Christ in 1846 more because of its stand on such political and moral issues as slavery, alcohol, and Freemasonry, rather than its theology.

Milton became an itinerant minister and one of the most outspoken members of the church, rising quickly within the church hierarchy. He fought against a liberalization of United Brethren doctrine on many issues. In 1869 he was appointed to the influential post of editor of the Religious Telescope, a weekly newspaper that carried official church views across the nation. He was ultimately elected a bishop in 1877.

A social reformer, Milton believed in equal opportunity for all. Both Milton and Susan benefited from parents who encouraged broad intellectual pursuits. They carried on this tradition with their own children.