Read it through once

The technique of the metaphysical poets, which is their most distinguishing characteristic, consists in the use of original and unexpected metaphors, in the concentration of thought, and in the boldness of the reasoning. The conceit, as it has been called, is not merely an ornament; it is the organising principle of the poem. The image is not decorative, but structural; it is the means by which disparate elements are welded together into a single pattern. The conceit often demands a subtle or recondite analogy; it is not content with obvious comparisons, but seeks a likeness which will illuminate the subject by a sudden and startling correspondence.