Which theme is best shown by the line "And I shall have some peace there, for peace comes dropping slow"?

These lines are taken from "The Lake Isle of Innisfree" by William Butler Yeats. The theme of these lines is related to the peace. The speaker might be feeling trapped, bussy, sad and that is the reason why his motivation in life is to achieve some peacefulness. So we can say that the main theme is: Peace.