The stanzas with shorter lines describe the making of the shield by the god Hephaestus, and report the scenes that Achilles' mother, the Nereid Thetis, expects to find on the shield and which Hephaestus, in Auden's version, does not make.
The stanzas describing the shield's creation by Hephaestus are accompanied by the expectations of Achilles' mother, Thetis, for what she will see on the shield, which Hephaestus, as per Auden's version, deliberately leaves out.