The speaker addresses a loved one, asking them to rest on their chest the way a covering rests over a boat. The image is quiet and protective, and the river moving underneath suggests a steady, endless current of feeling. The poem keeps saying "not this, but that": not the sun, but its warmth; not the rain, but the passion of rain. Love here is felt as an atmosphere rather than as something you can point to.
The middle lines, "Not in touch, yet touching," capture the odd position of the boat itself, floating a little way from the shore and a little below the skyline, belonging fully to neither. That in-between state seems to describe the relationship too: close, but not quite held. In the final stanza, the beloved's presence blends into every hour, day or night, dark or moonlit, until it becomes part of how the speaker senses life itself. The mood is dreamy, tender and calm, with a faint ache of distance.