This poem is about the "ritual sacrifice" of death as part of the natural order of living, particularly as seen against the backdrop of the ocean, which although beautiful on the surface, camouflages dangerous forces which have cost humans their lives for centuries. Toward the poem's end, Spender refers to "voyagers. . .set forth from some island/And them the seas engulfed." The heat of the afternoon, the ocean, the march toward death of all living things. . .all these things are unmoving, unchangeable, and Spender establishes their permanence even as he creates imagery of movement in the ocean, the air, and in life.
In some ways, this poem could be considered similar to Robert Frost's "Stopping by Woods on a Snowy Evening". Frost used the imagery of a forest, "lovely, dark and deep" as a metaphor for death, luring the rider of the horse, who nonetheless presses on because he has "miles to go", in other words, many things to accomplish, before he can sleep. The permanence of the still, beautiful forest, upon closer inspection, camouflages dangers awaiting the rider, who for now will continue moving, but ultimately will return to the woods when his life is over. Similarly, Spender's ocean imagery focuses on something that is externally gorgeous, internally dangerous, and will ultimately triumph over all human life.