Sub-dividing the Sermon 

First spot the structure

Complex mesh of supporting struts in an intricate pattern around a central column.
The supporting framework of Pater Noster, a Swedish lighthouse.

As in the Pater Noster lighthouse, repetition is an obvious structural feature of the Sermon on the Mount. But to focus solely on repeated elements is to overlook other important structural features, such as a sequence of themes that mirrors the sequence in a foundational text or the use of more complex poetic structures.

The way you sub-divide the Sermon on the Mount into more manageable pieces is important, because it can give a verse a completely different emphasis. Get it badly wrong and you can miss the point entirely. The sensible approach is to first identify the underlying structure, then break that apart along its natural seams. However, it is not quite that easy with the Sermon, for it can be treated as: 

The identification of multiple structures within the Sermon does not mean that only one is right or that only one is original. The three structures identified above appear complementary and therefore deliberately designed to allow this incredible piece of teaching to say different things depending upon how you approach it. As the three structures interlock, they demonstrate that the text is much more than a simple collection of sayings that one can pluck out and examine in isolation. Though, as any analysis of parallel gospel passages quickly reveals, many sections of the Sermon on the Mount happily lend themselves to re-use in other contexts.