In my Ko-Fi Shop: The Interior or Hidden Life by Thomas C. Upham (1799–1872).
In his book on Upham’s theology, Darius Salter wrote:
“Upham’s writings are the first attempt to weigh the tenants of holiness theology within the rubrics of psychological investigation. His findings are integral to the history of the psychology of religion. Upham’s Principles of the Interior [or Hidden] Life (1843) may be the best attempt to stress experiential holiness theology within a psychological context.”
