Both Sylvia and the white heron are reclusive children of nature.
What a spirit of adventure, what wild ambition! What fancied triumph and delight and glory for the later morning when she could make known the secret!
It is, indeed, because she is one with nature that Sylvia cannot reveal the secret home of the heron. For, telling the young man will be a betrayal of the heron, a kindred creature so like the "lonely country child."
For Sylvia the white heron is unique and it symbolizes the freedom she has known in the country. Betrayal of this free spirit means its death; and, if Sylvia causes this death she will have guilt and no longer be free herself. Because the bird has provided Sylvia with the vision of the sea and world beyond, the girl cannot be the cause of its death.
In an essay, "A White Heron: Sylvia as Hero in Sarah Orne Jewett's 'A White Heron,'" the author quotes a work written by Joseph Campbell, which treats the hero archetype who receives a call to adventure, then the hero is invited into "an unsuspecting world" where there are forces which help him/her.
Sometimes this victory is accompanied by a mystical vision that shows the hero something of the life-creating energy of all existence.
This vision, then, takes the hero through a succession of trials into a victory in which the hero crosses into a "dimension that vanquishes all opposition." Sylvia has Just this transcendental experience and cannot, therefore, betray the heron to the mundane and banal world.