A little graphic I put together explaining the threefold division of the noble eightfold path.
The simile of a pyramid came to me to explain the relation between the three divisions. Your whole practice rests on a firm basis of Sila, or virtuous living. Like any structure being built, it relies on the base to act as a firm foundation.
Upon this firm foundation rests our meditative and contemplative practice, and upon that practice rests the capstone of the Noble Eightfold Path – the Wisdom/Insight division of the path.
virtuous living –> concentration –> insight –> liberation.