What's the main idea of this poem? "Meeting at Night"

The gray sea and the long black land;
And the yellow half-moon large and low;
And the startled little waves that leap
In fiery ringlets from their sleep,
As I gain the cove1 with pushing prow2,
And quench its speed i’3 the slushy sand.

Then a mile of warm sea-scented beach;
Three fields to cross till a farm appears;
A rap at the pane4, the quick sharp scratch
And blue spurt of a lighted match,
And a voice less loud, thro’5 its joys and fears,
Than the two hearts beating each to each.