Narratives cohere (often) around a central character or set of characters. Or, as in a saga, like D.H. Lawrence's The Rainbow, several generations of people living in the same place provide the threads of interconnection between the succesive stages of the novel. One novel I read, Annie Proulx's Accordian Crimes, coheres around an inanimate object (an accordian) as its finds itself in successive sets of hands. In Anna Karenina two plots are interwoven though there is little connection between them - they are connected in that the characters share in family relations of a somewhat distance kind.
Ultimately, it is the collecting of the elements together in the single work that unifies them, though usually there are more elements of formal coherence than that. Think of a painting in an art gallery: it is the framing and placing of the elements within the frame and on the wall that invites us to consider them as a unity, even if the elements of the painting are quite discordant. If they are discordant, we tend to ask why they have been juxtaposed and wrestle to discover what relation there might be or that we might find between them.
These formal coherences - often unimportant in themselves - invite the reader to consider and discover thematic coherences as suggested by the stories. Sometimes these are quite surprising, granted. Sometimes the formal coherences do not account for all the elements in the work, at least not obviously. But the human love of comparing and contrasting, and of finding patterns, makes for the most enjoyable part of engaging with narrative art forms.
The other aspect of our apprehension of coherence when it comes to narratives is of course time. We experience time in narratives through emplotment. No matter how many post-modern novels cut and paste their narratives, the narrative form relies heavily on a succession of events and invites us to consider (or tells us) what the relation between the events consists in. EM Forster famously wrote: 'The king died and then the queen died is a story. The king died, and then the queen died of grief is a plot.'
The canonical Bible has a coherence in a formal sense in the first instance in that it traces the history of Israel with its God in a roughly chronological order. The New Testament claim is that it continues and indeed completes this history. However, there are things that are collected within the lists of Law, Writings and Prophets that are not obviously part of the main succession of events. Very few clues are given as to why Job, for example, has been placed within the canon: which is for us readers an invitation to consider what it does contribute. It is almost as if it has been placed there by intuition: (from the human side) by an editor not quite knowing what he was yet looking at but sure that what he had was of inestimable value, and recognising in it the divine voice.
I suppose what I am leaning towards saying is this: the formal unity of the Bible consists of the collecting of these books together as Scripture; and its relation to salvation-history. The Bible describes a series of events that were connected to one another over time, in place, and by a people connected intergenerationally. This formal unity allows then for multiple strands of thematic coherence to be discerned, some of which are more prominent and others less so, and which have complex relations to one another. Of course, some of these coherence is quite obvious, as the authors of scripture deliberately cite each other, and play with and develop - even critique - the themes and other content of other scriptural books. This is also why it is inadequate to read any passage of scripture without due consideration to its relationship to salvation-history and without relation to how the particular themes within it are treated and developed within the canon.


