One from a lucid urn of starry dew Wash'd his light limbs as if embalming them; Another clipp'd her profuse locks, and threw The wreath upon him, like an anadem, Which frozen tears instead of pearls begem; Another in her wilful grief would break Her bow and winged reeds, as if to stem A greater loss with one which was more weak; And dull the barbed fire against his frozen cheek.
The goddesses have arrived to prepare the body. This stanza stops calling out to the mourners and instead focuses on this mournful preparation.
One of the goddesses uses a clear urn (container) of "starry dew" to wash his limbs. Even the youth's corpse is treated to other-worldly pleasures.
The speaker imagines these preparations taking place in a fantasy world, which may be the only place he thinks is appropriate for someone as beautiful and pure as Adonais-Keats. Here on earth, we just can't do the youth justice.
Another goddess cuts her hair off to make a wreath ("anadem") for his head.
Then yet another goddess uses her frozen tears, instead of gems, to adorn ("begem") the body, and another breaks her bow-and-arrow out of grief. (That's our clue that the speaker intends these women to be the goddesses; the bow and arrow belongs to Artemis, goddess of the hunt.) She does this to focus on a lesser loss, to override the effect of the youth's death on her ("dull the barbed fire against his frozen cheek").
Adonais must be important, if he has such big-name goddesses so upset about his death.
The speaker would know that no such preparation of Keats' body occurred in real life, but he thinks he deserved it anyway. Perhaps by putting it into the poem, he can make it real in the same way that he gives Keats the power to make dreams into poetry.