How does Mary Stewart use imagery in The Crystal Cave?

Imagery:

"They used to say in my country, the ring-dove has many enemies, because her flesh is sweet and her eggs are good to eat. But she lives and she prospers, because she runs away. The Lady Niniane may have called you her little falcon, but you're not a falcon, yet, young Merlin. You're only a dove. Remember that. Live by keeping quiet, and by running away. Mark my words."

"So all through that winter he came to me. And he came at night. I was never alone in my chamber, but he came through doors and windows and walls, and lay with me. I never saw him again, but heard his voice and felt his body. Then in summer, when I was heavy with child, he left me." Book Three, Chapter 8, pg. 295