The words that help the reader visualize the scene are "against the morning’s white" and "Toward the summer isle."
"Against the morning’s white" evokes a clear image of a bright, crisp morning, and "Toward the summer isle" suggests a vivid, tropical location, enhancing the visual imagery of an idyllic, warm place.
While "Some day" and "We’ll turn our faces" contribute to the sense of time and action, they are less focused on creating a visual image than the other two phrases.