Two Themes That Affect Marlow and Kurtz In Heart Of Darkness There are many themes that run through the novel Heart of Darkness. There are however two main and significant ones. These are the theme of restraint and man's journey into self. The importance of restraint is stressed throughout Heart of Darkness. In the novel Marlow is saved by restraint, while Kurtz is doomed by his lack of it. Marlow felt different about Africa before he went, because the colonization of the Congo had "an idea at the back of it." Despite an uneasiness, he assumed that restraint would operate there. He soo