McGary became interested in religion and studied the Alexander Campbell - Robert Owen debate of 1829.
[1] He was said to have been educated in part by Church of Christ ministers including Benton, Thomas, and Basil Sweeney.
[2] McGary was converted to the Churches of Christ and baptized by Harry Hamilton after hearing sermons by the latter in Madisonville, Texas.
He began publication of the Firm Foundation in 1884, in his own words: In debates with David Lipscomb, editor of the rival publication Gospel Advocate, McGary advanced positions regarding the relationship between baptism and salvation, some of which were already seminal[3] in the formation of the group of Christian churches known as the Churches of Christ, others of which would become the basis for continuing disagreement among members of that body.
The substance of McGary's argument was based on the notion, generally accepted by members of the Churches of Christ, that the state of human salvation begins at the moment of that individual's baptism.