The speaker of the poem is describing his feelings, mainly his desire to get back on the sea again. He wishes to be on board a tall ship, helping to steer the ship with only the light of the stars. He misses the look of the sea. The speaker says that the sound of the tide is a call to his soul that he cannot refuse, and he longs for the wind and clouds, the sea spray and the sea gulls.
He longs for a nomadic life, comparing the wind, via simile, to a whetted knife. A simile is a comparison of two unalike objects where one is said to be like or as the other. A whetted knife is a sharpened knife, and so the simile seems to comment on and emphasize how sharp the wind is on the sea. This comparison makes it seem as though the touch of the wind can be painful. The connotation of a sharpened knife is a somewhat dangerous one, and so this comparison seems to nod to the dangers of life on the sea. Given the way the speaker describes the sea throughout the rest of the poem, it seems as though he adores it, and so perhaps the element of danger is something that he actually misses as well.