The poet writes that while composing poetry he thinks back on times he talked at the fireside of "the dark men" - i.e. the dark urges and warlike deeds - within passionate people. They also discuss the mix of sorrow and content that comes with a passionless life, and of the music of swords on the battlefield.
This poem anticipates some of Yeats's later work (especially after he began to be influenced by Ezra Pound) in its spareness and its lack of specifically Irish allusions. The poem is bleak and full of ambiguous images, spilling from descriptions of the ways men engage battle to a weird bat-like image at the poem's end.
The poem can be read as a reflection on Yeats' own writing. It begins, "When I wrought out these fitful Danaan rhymes," inviting us to consider the poem as a document of Yeats' imaginative process. Indeed the poem touches upon several of the identities captured in the preceding poems - the passionate dark individualist, the sorrowful resigned soul, the multitudes at battle. And through it all, Yeats spins eerie images of bats and animals, which seem both to refer to his poems about communion with nature, but which also seem like expressions of pure, inexplicable imaginative fire. He is capturing for us - performing for us - the free-associative brilliance that makes his poetry so challenging and rewarding.
On a more concrete level, the "blossoming dream" is possibly an allusion to Irish Republicanism. The 'Republic of Eire' was a name that could not be spoken in Ireland, as it had dangerous nationalist connotations. Hence the description of the multitudes rising up in battle with the 'Ineffable Name' on their lips, which might well represent the Republicans striving against England for liberty.