What does the poet mean by the lines "may the poison purify your flesh of desire and your spirit of ambition" ?
This poem is by an Indian poet, Nissim Ezekiel, and it reflects Indian culture. A woman, the poet's mother, has been bitten by a scorpion and its poison is flowing through her body. Holy men come in and pray over the woman to cure her. The line you refer to is part of their prayer:
May he sit still, they said.
May the sins of your previous birth
be burned away tonight, they said.
May your suffering decrease
the misfortunes of your next birth, they said.
May the sum of all evil
balanced in this unreal world
against the sum of good
become diminished by your pain.
May the poison purify your flesh
of desire, and your spirit of ambition,
They are hoping for the mother to be cured, but just in case she is not, they are praying for her as she goes into the next world, and is reincarnated (part of the Indian's beliefs). This line means that if she is to die from the poison, at least let it purify her of any sin so that when she is reincarnated, she won't come back to life as a cockroach or some lower form of life. Hindus believe that if one does not live a good life, he will be reincarnated as a lower form.
I think this line is ironic, though, because the mother does not have any "flesh of desire" or "spirit of ambition" because in the end, she thanks God for the fact that the scorpion bit her and not her children.