What does this line mean in the poem 'La Belle Dame sans Merci'?

What Keats wishes to convey in this line is her utter freedom from worldly convention, but the iconography is itself fully consistent with the broader interpretation of the poem as a whole. Let me offer you what I consider to be the best available interpretive axis for this and several other poems by Keats, Keats's 'Beautiful Lady Without Kindness' is not, by extension, an embodiment of evil or antithetic to kindness; she is an embodiment of the daemonic, a concept that fascinated Keats, one drawn from the clical Greek philosophers, and she exists beyond the ordinary diurnal polarities of good and evil that we customarily use to understand our world. She is spirit, and by transporting the knight to her otherworldly grotto and feeding him the dainties of the other world, she essentially leaves him suspended between the warmth of home and hearth most men would naturally seek in the season when the granary is full and the sedge has withered from the lake, and the world of bliss she inhabits. He cannot, as mortal man, subsist in her realm, but having tasted her delights, in their manifold forms, come fully back to the mundane world into which he was born. He lives, effectively, between two worlds, and when he sees the starveling visions of her other suitors, he is made aware of the alarming consequences of his encounter, and yet is unable to resist her. He has achieved a measure of actualization otherwise unavailable, and has been destroyed by it! Thus, La Belle Dame also becomes an image of the poet's muse, who similarly seduces him, and transports him to a world in which he can partake but never permanently reside; she represents, in some sense, both vision and an altered state of consciousness, but the truest touchstone is the clical conception of the daemonic, one more richly explanatory than the biographical facts of Keats's life often adduced to explain this remarkable poem! I hope this brief explanation has begun to set your feet on the path to a richer understanding of Keats's unique genius... I do not use the world lightly in his case.