What is the message of the poem "Leda and the Swan," by W.B. Yeats?

In "Leda and the Swan", Irish poet William Butler Yeats
takes the traditional form of the Petrarchan sonnet and fills it with an image evoking a
powerful aesthetic experience. The image is Zeus's rape of Leda, in Greek mythology,
daughter of Thestios, king of Aetolia, and wife of Tyndareus, king of Sparta. Assuming
the form of a massive swan for the violent seduction, Zeus fathers the twins, Castor and
Pollux, and Helen of Troy, peerless in beauty in all the world. This moment of
conception, rendered in the sonnet's transition from the octave to the sestet as "a
shudder in the loins" conveys the principal message of the poem: Leda's
savage impregnation is the genetic blueprint for the Trojan War - "the broken wall, the
burning roof and tower
and Agamemnon dead" -  the rise of Greek civilization,
and the unfolding  history of the West. The poetic transition in fact objectifies the
end of the mythological world and the beginning of history.