The poem opens as the clock strikes midnight, setting up a quiet, nocturnal atmosphere when most people would be asleep. A number of stanzas start in the same way—with a reference to the time—which helps establish the speaker's diminishing sense of control as the night wears on. Midnight is particularly associated with the supernatural, and so here hints at that loss of control to come.
Lines 2-6 suggest a dreamlike blurring of the boundaries between time, the speaker's memory, and the world itself. Line specifically 2 establishes the urban environment through which the speaker walks, while lines 3-6 suggest that this environment is under some kind of spell, perhaps cast by the moon.
Indeed, the street seems to be "held" in the moonlight, the assonant /l/ sounds linking "held" with "lunar." It's not too clear yet what is actually going on in the poem, but things certainly seem dreamlike and somewhat unnerving. And already the question of who is in control—the moon, the speaker, or someone/something else altogether—is starting to be asked.
Line 4 introduces the idea of "lunar incantations." An incantation is a kind of spell or charm, suggesting that the usual logic of the world can be undermined late at night. In other words, the night makes ordinary things—the same street that the speaker has perhaps walked down casually during the daylight—seem strange, mystical, or foreign. Sibilance throughout these lines—especially apparent with the /s/ and /sh/ sounds in words like "whispering," "synthesis," "dissolve," "relations," and "precisions"—adds to the hushed, mysterious quality.
Throughout history, the moon has been associated with magic and witchcraft, both of which are ways of disrupting the way the world usually works. But it's not clear who or what is actually doing the whispering here—the syntax of the lines allows for the source of the "incantations" to be disembodied (that is, it's not explicitly connected to a subject). However, the most likely source of these magical "incantations" seems to be the moon itself. That is, rather than a person appealing to the moon for supernatural assistance, here the roles are reversed: the moon offers incantations of its own.
Lines 5-7 make clear the effects of these "incantations." Namely, they:
Dissolve the floors of memory
And all its clear relations,
Its divisions and precisions,
In other words, these spells destabilize the certainties of the speaker's human existence. Memory, rather than being kept in a little box or room in the mind, is starting to seep into the speaker's lived experience of the world, blurring the line between reality and imagination. The assonance of /o/ sounds ("dissolve the floors of memory") creates a feeling of slowness that mimics this process of dissolving.
Likewise, the matching "-ion" suffixes on "relations ... divisions and precisions" links these words together sonically—they are all part of the way in which human beings usually make sense of the world, and are under threat in the darkness of the night.