The Testament of Gideon Mack was inspired by two influential Scottish works from the 19th Century:
James Hogg's book tells the story of Robert Wringhim. He is brought up to follow an extreme form of Presbyterianism that proposes that some people have already been chosen to have a place in heaven, regardless to how they lead their lives. Wringhim's beliefs lead him to commit murder.
There are a number of similarities between the “The Testament of Gideon Mack” and Hogg’s “Confessions” which emphasise the degree to which Robertson was influenced by this novel.
Robert Louis Stevenson’s novella about a doctor who has split personalities has parallels in the character of Gideon Mack. Gideon is a "chameleon", with the ability to adopt different personas throughout his life. This ability enables Gideon deceitfully to convince his parents and then his congregation that he is a devout Christian, despite holding strongly agnostic beliefs.
Both books deal with ideas of differences between a person's private and public personas, and with controlling or giving in to emotional impulses.
The novel begins with an extract from Black Rock of Kiltearn written by the 20th century Scottish poet Andrew Young, who was also a Church of Scotland Minister.
In the poem, Young imagines falling into a gorge in the Scottish Highlands, dying and then being resurrected.
There are obvious similarities here to the character of Gideon Mack, particularly as Gideon is “reborn” as a new man after his accident at the Black Jaws.