Who is Professor Henry Drummond from Rees Howells: Intercessor and what is their importance?

Drummond is the author of the book, Natural Law in the Spiritual World, which is the book Rees is reading while living in Ohio. When Rees was reading Professor Drummond's book, many questions came over Rees. The book, together with what his cousin asked him, changed Rees' world and made Rees aware of the spiritual distance between Rees and God. They also gave Rees concern about where he would spend eternity.