I'd say, in relation to the angel reference in this poem, the whole section involving angels and clay could be interpreted as having a certain meaning in a religious sense. Obviously the old cliches are there, the creation of man from clay in God's image, the angel, are classic representations of religion in poetry. Man, made of clay, and angels, the heavenly choir, are not supposed to engage with each other and through these constructs Kavanagh is, by way of my interpretation, attempting in these few lines to grapple with the topic of self sacrifice. for an angel to lose his wings is a fall from grace with god, and this happens because of wooing the creature made of clay. Kavanagh is trying to show that the love he is reflecting on in this poem is one which the protagonist is willing to sacrifice all he possesses, even grace with god, to fulfill.