can anyone explain the poem

SNOWMEN

My ancestor, a man
of Himalayan snow,
came to from ,
carrying a bag
of whale bones:
heirlooms from sea funerals.
His skeleton
carved from glaciers, his breath
arctic,
he froze women in his embrace.
His wife thawed into stony water,
her old age a clear
evaporation.

This heirloom,
his skeleton under my skin, passed
from son to grandson,
generations of snowmen on my back.
They tap every year on my window,
their voices hushed to ice.

No, they won't let me out of winter,
and I've promised myself,
even if I'm the last snowman,
that I'll ride into spring
on their melting shoulders.

--Agha Shahid Ali, from The Half-Inch