A cold, lonely speaker sets out toward the sun, and the poem is built from that simple urge: to find warmth and to go and get it. The speaker travels "all alone," which makes the journey feel both brave and a little sad.
What they find is strange. The sun sits "at sea," and the poem offers two comparisons for it. First it is like a dinner being brought to the table, something warm and welcoming, yet the speaker "could not interpret" it, as if the comfort is there but not quite understood. Then it becomes "the first walk on water / by a dark swan," a surprising image where a dark bird glides out onto the surface, perhaps mirroring the sun's dark silhouette or reflection on the waves.
The mood is quiet, dreamlike, and a bit mysterious. There is longing for warmth, but also a sense of wonder and uncertainty. The poem doesn't explain what the sun means, and that open-endedness is part of its pull.