This is a poem of love and nostalgia for one home's country. Wordsworth wrote it after travelling abroad for some time, and finding that when he went abroad it was not the exciting experience that he thought it would be. He describes it as moving "among unknown men" which indicates how lonely he felt. The first stanza balances this experience of travel with an evocation of the love that the speaker has for England in the second half with England being apostrophised.
Now that the speaker is back in his beloved England, he looks back on his foreign travel as a "melancholy dream" and swears that he will never leave England again because the love he has for his country is just growing greater and greater. It was only among the mountains of England that Wordsworth felt "the joy of his desire" and also Lucy, the subject of Wordsworth's longings and unrequited love, is a figure who is rooted firmly in English soil. The fact that Lucy lived, played and died in England is another factor that makes England so important to the speaker:
Thy mornings showed, thy nights concealed
The bowers where Lucy played;
And thine too is the last green field
That Lucy's eyes surveyed.
Not only does the speaker have a strong connection with his home country but he also has another attachment as England is the location where he loved and lost his beloved Lucy. The connection that he feels to her even after her death is something that makes England forever special in his mind.