I looked in my heart while the wild swans went over.
And what did I see I had not seen before?
Only a question less or a question more;
Nothing to match the flight of wild birds flying.
Tiresome heart, forever living and dying,
House without air, I leave you and lock your door.
Wild swans, come over the town, come over
This gives the swans status, and meaning can be drawn from them — beauty, the mystery of flight, for example. 
 Continuing the repetition, the poet uses ‘flight’ and ‘flying’, a noun and a verb respectively. The trope of flight to represent freedom is much-used in poetry.
Wild Swans