Light is supposed to be the weightless thing, and that is the first trick of this short poem. It opens with "all light must sink," and the line feels wrong before it ends. Light rises, spreads and fills rooms. Here it obeys gravity, and the word "must" turns the sinking from a choice into a law. By the time the second line names the destination, "into a hole," the poem has taken away our usual comfort in brightness.
On the surface, the poem describes a descent, first of light and then of the speaker. Underneath, it is about surrender: the pull toward giving up effort and letting oneself fall. The title, "The descent beckons," personifies the fall as something that calls to us, almost politely. The central idea is that this invitation is dangerous because it is easy. The second stanza says so directly: "a descent made easy / and leaden / should I let go." The poem never says what the hole is. It could be despair, sleep, death or just the end of a day. Judging by the imagery, it cares more about the feeling of the pull than about its cause.
The form is bare. There are two tercets, no punctuation and no capital letters, so nothing marks where a thought stops and the next begins. The poem has no rhyme in the strict sense, but "hole" and "go" share a long, falling vowel across the stanza break, and the sound lingers like an echo down a shaft. The line lengths are worth counting. The first stanza runs four syllables, four, then six. The second runs six, three, then four. The two longest lines sit on either side of the stanza break, so the poem swells at its centre, then thins out and drops away. The opening line is four near-monosyllables, "all light must sink," each demanding its own stress. It moves heavily, as if the words themselves were being dragged down. "Into a hole" is quicker and lighter, so we seem to slip in before we notice.
The most surprising image is the simile "weary as walking fish." The poem could have compared the light to a stone or a setting sun. Instead it gives us a fish hauling itself across land, like the mudskipper, which really does crawl out of water. The comparison is odd and a little comic, but it carries the poem's mood. A walking fish is out of its element and every movement costs effort. The soft repeated "w" sounds of "weary" and "walking" give the line a slow, plodding drag. There is a quiet irony too. Walking fish suggest the ancient journey out of water onto land, and here that effort ends in a descent. The weariness is that of something that has struggled upward for a long time and is ready to stop.
The last stanza turns on the word "leaden." Lead is the opposite of light, so the poem plays on the double meaning of "light" as brightness and as lack of weight. The word also contradicts "easy." We expect an easy descent to feel like floating, but here it feels heavy, and the ease comes from the weight itself. Giving in requires no effort, because gravity does the work. "Leaden" also stands alone on its short line, three syllables, the briefest in the poem, and it lands with a thud.
The final line changes the poem's grammar. Until now the subject was the impersonal "all light." Now it is "I." "Should I let go" is an inverted conditional meaning "if I let go," but "should" also hints at obligation, as if the speaker were asking whether he ought to. The poem ends on "go," an open vowel with no full stop, and the reader is left hanging at the edge of the decision.
That restraint is what makes the poem worth reading. In twenty or so words it sets the physical and the emotional side by side, so that a falling beam and a tired mind seem to be the same event. It does not say whether the speaker lets go, and it does not reassure us either way. It leaves us feeling the pull, and the smallness of the poem makes that pull easier to recognise.