The present volume has employed a mosaic pattern of perception and observation up till now. William Blake can provide the explanation and justification of this procedure. Jerusalem, like so much of his other poetry, is concerned with the changing patterns of human perception. Book II, chapter 34, of the poem contains the pervasive theme :
If Perceptive organs vary, Objects of Perception seem to vary;
If Perceptive Organs close, their Objects seem to close also.