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 with shorter lines detail Hephaestus' creation of the shield, as well as the scenes that Achilles' mother, Thetis, anticipates seeing on the shield, which Hephaestus, according to Auden's version, fails to include.