Why doesn't the story fit? I mean, the song is a love song sung by a boy of the wrong class or religion to a girl, after he's come visiting, and has been put winding the straw rope with her, so that he will have to back away gradually from her out the door of the house and across the haggard, so he's singing -

If you are mine, be mine, o treasure of my heart If you are mine, be mine in front of all the world If you are mine, be mine every inch of your heart And by my naked word, you will be mine on Sunday as wife.