The title of this novel is an interesting insight into the meaning of the plot. The idea seems to be that England was the "Babylon" of this period, that English settlements might have remembered their lives in Europe in a way that predisposed them to mistreat foreigners, by way of white supremacy which devolves into full-blown paranoia and rejection of foreigners altogether.
The idea of Babylon is an allusion to a book in the Bible called the Book of Revelation. In that scripture, a prophet sees an ecstatic vision of the apocalypse and he describes in poetry, and in some of the chapters, the prophet talks about Babylon as a metaphor for whatever world power is most powerful at a given time. So during the 1850's, Babylon was England, since they were the most powerful. The implication therefore, is that since the settlers are an extension of that dominant culture, that their attitude toward other people and toward nature is inherently evil, as if they are remembering Babylon in a way that prevented them from seeing Australia for what it really is, and for understanding their relationship to the land and native peoples of Australia. The reason they're evil is because they are proud of their supremacy.
But to the ones among them who are still open-minded enough to be influenced by Gemmy's way of viewing the world, Gemmy becomes like a Messiah to them, unlocking their potential through his insight, even though he was rejected and abused by them. To understand Gemmy as a Christ-character just makes sense, given the overt Christian overtones of the work, and the fact that Gemmy's influence in Janet's life means that she transcends herself and joins a convent.
Janet's conversion story is perhaps one of the novel's clearest depictions of its intent. By reframing Janet's perspective about nature, Gemmy gave Janet the ability to perceive her own pain as part of the natural process, and she is religiously enlightened by that experience. In fact, she has an epiphanic, nearly ecstatic moment and gives her life to serving others. There's a pretty clear moral theme to that story, that through humility, we can transcend fear and attain a higher mode of consciousness.
