The poem sets love against the comfort of darkness. Love is called a "strange sun" and "a white bear lost at sea," two images of something huge, bright and out of place. A polar bear far from ice is both powerful and helpless, and the poem seems to say love can be the same.
The speaker sounds calm, even guarded. Angry words don't trouble them, and they like the dark. That reads as a kind of protection: if you stay out of the glare, nothing can hurt you much. But the last stanza turns this around. Too much light makes the eyes "believe vicious and impossible things," as if intense feeling distorts what we see. The closing image of "little kings making a peace out of the dead" suggests a hollow, bitter kind of victory, with calm built on loss.
The mood is cool, wary and a little unsettling. Love here feels less like warmth than like something dazzling and dangerous.