Three short lines, and a whole small scene opens up. Someone says "our reflections" are in the window, so there are at least two people, the speaker and someone else, standing or sitting together and looking at the glass. The word "our" matters. The speaker doesn't say "my reflection" or "your reflection." They see themselves as a pair, sharing the same frame.
The mood is quiet and a little wistful. A reflection is not quite real: it's faint, see-through, and it vanishes when the light changes. By placing "our reflections" in the window rather than the people themselves, the poem hints that this togetherness might be fragile, or that the speaker is looking at it from a slight distance, almost as if watching it happen. The poem never says what the speaker feels outright. Judging by the stillness and the spare wording, it seems like a moment of calm noticing, tender but touched with the sense that it won't last.