The poem is built from a few strange, quiet images that add up to a feeling of longing with nowhere to go. In the first lines, passion is compared to a river empty of boats: full of force and movement, but carrying nothing and no one. The speaker seems to have a lot of feeling and no outlet for it.
The next image is just as hopeful and just as odd. Holding a wine glass out for rain and a napkin for ink suggests someone waiting to be given something, whether it's a drink, a sign, or the right words, using tools that are far too small or wrong for the job. There's a gentle, rueful humor in it.
Then comes the turn. The speaker stops writing letters and "died in her bed." The death may be literal, but it more likely suggests surrender, a love so complete that the old way of reaching toward her, through words, is no longer needed. The mood is tender, wistful, and a little wry.