Final answer:
Keats immortalizes Psyche's beauty and love through his unwavering devotion and poetry.
Step-by-step explanation:
In Keats's "Ode on a Grecian Urn," he does not explicitly mention how Psyche will become eternal. However, through his unwavering devotion and poetry, Keats immortalizes Psyche's beauty and love in the artwork of the urn. By capturing her essence in his words, Keats ensures that Psyche will live on forever in the minds and hearts of those who appreciate his poetry.