A person goes out walking at night, and the reason is surprisingly gentle: the dark is kind to their eyes. Maybe the day has been too bright or too busy, and the night offers relief. The speaker has nowhere particular to go, only the garden, which is the one place left to turn to. That small detail makes the scene feel quiet and a little enclosed, as if the whole world has shrunk to a few plants and some shadow.
Then the last stanza shifts. A "second sun" appears and makes the speaker "see." The poem never says outright what this light is, though the title suggests the moon. What I find striking is that the moon is treated as a rival sun, one that lights things up without the glare. The mood is calm, hushed and slightly mysterious. The speaker seems less lonely than soothed, and the ending hints at a kind of clear, gentle awareness that only comes after the daylight has gone.