How does Willa Cather use imagery in The Professor's House?

Imagery:

"But the notes and the records and the ideas always came back to this room. It was here they were digested and stored, and woven into their proper place in his history."

"St. Peter lay looking up at them from a little boat riding low in the purple water, and the design of his book unfolded in the air above him, just as definitely as the mountain ranges themselves. And the design was sound."