What is Mary Robinson's "Marie Antoinette's Lamentation in the Prison of her Temple" about, and what is she trying to say or convey through the poem?

In the poem "Marie Antoinette's Lamentation in the Prison
of her Temple," Mary Robinson (the author) tries to capture Marie Antoinette's last
hours, as the Queen of France laments her captivity and her fate.  Marie is confused
that life continues to move forward the same as it always has, even in light of the
recent events that have changed her future forever, while she agonizes greatly over the
impending separation from her children, and their fates.

At
the start of the poem, Robinson, speaking as Marie Antoinette, refers to the beautiful
light of the setting sun that rests across her body through the barred windows of her
cell.  Even as life is so terrible, and Marie is so filled with sorrow that her tears
have stained the front of her dress, the sun moves as it does each day.  Marie asks that
if the meanest  and poorest child can find an hour's peace at night, why can
she not have that peace as well. It seems that no matter where she
places her head, it lies upon a bed of thorns (though it has not been too long ago, that
it was a bed of roses)...

And when the sun comes up again
the next morning, the birds sing as usual. She recalls other mornings when her life was
so different. She mourns that this will soon be lost to her, as will the sight of her
sleeping children. The idea drives her to weep and clasp her children wildly in her
arms.  She states that the hands which will come together to rip her children from her,
are inhuman. She sends up a prayer that these hands will stop long enough for the
infants to rest a while longer in their mother's company, she who is now a widow—perhaps
to even let these small ones grow a while.

Outside the
cell, Marie can see the play of lightning's brightness across the walls.  Her children
cry, and then sleep, unaware of their mother's "frantic fears." She believes no harm
shall come to them because they are innocents.  In her state of dejection, she can hear
the bells ringing outside, the raucous songs sung for the Revolution, while the cannon
fire explodes in the sky.

Marie Antoinette finally pulls
herself together.  She resolves to meet Death steadily, bravely.  Still, she is haunted
by thoughts of her "friendless children," and her maternal instincts will not let her
rest.

Everywhere she looks, Death is drawing nearer.  At
this point, the author writes "they pierce, with many a recreant sword, the mangled
bosom of my bleeding Lord."  I cannot be sure if this refers to the crucifixion of
Christ or to the death of her husband, (though he was actually
beheaded, the only French king to be executed in the country's history).  In either
case, this thought causes her great agony.

Marie, even
while trying to be brave, wonders when this bloodshed will end, and when will
she be released into "sweet Oblivion's dream," to a more peaceful
place? And she wonders also (using personification) if Pity will break the hold of Death
and release one prisoner from its final
snare?