Out of her secret Paradise she sped, Through camps and cities rough with stone, and steel, And human hearts, which to her aery tread Yielding not, wounded the invisible Palms of her tender feet where'er they fell: And barbed tongues, and thoughts more sharp than they, Rent the soft Form they never could repel, Whose sacred blood, like the young tears of May, Pav'd with eternal flowers that undeserving way.
The speaker says that Urania was in a good, happy place; he describes it as "Paradise." But her grief was so great that she could not stay.
Her quest took her all over the place, but the one place that didn't let her pass easily was the human heart. So what's that all about? It sounds gory. The last time we tried to pass through a human heart, it was not pretty…
Actually, the speaker is using figurative language here to compare the public's lack of reaction to the hardened hearts that Urania's grief cannot penetrate. He's pretty mad that the public didn't seem to care much that Adonais-Keats died.
It doesn't end there, though. The speaker mentions the "barbed tongues" and "sharp thoughts" that also repelled her grief. The sharp thoughts and spiky tongues refer to criticism, which, you may remember, is what Shelley believed really killed Keats.
Ouch—suddenly, the poem has taken a more pointed tone. Our speaker doesn't just want us to grieve; he wants us to feel badly for criticizing, or even just ignoring, Keats.
He says the public is "undeserving" of Keats' "eternal flowers," or his beautiful, eternal poetry.