What does Marley's comparison of kindness to the first green grape of summer mean?

Read the excerpt from act 3 of a doll’s house. mrs. linde: you seemed to me to imply that with me you might have been quite another man. krogstad: i am certain of it. mrs. linde: is it too late now? krogstad: christine, are you saying this deliberately? yes, i am sure you are. i see it in your face. have you really the courage, then—? mrs. linde: i want to be a mother to someone, and your children need a mother. we two need each other. nils, i have faith in your real character—i can dare anything together with you. krogstad [grasps her hands]. , , christine! now i shall find a way to clear myself in the eyes of the world. ah, but i forgot— how does the conflict in this passage develop a theme? mrs. linde creates a conflict by promising something she cannot give to krogstad, which develops the theme that empty promises can destroy relationships. krogstad continues the conflict by choosing clearing his name over having a life with mrs. linde, which develops the theme that you must often choose yourself over others. krogstad creates a conflict by deceiving mrs. linde about his intentions, which develops the theme that, in love, actions speak louder than words. mrs. linde resolves the conflict by committing to a new life with krogstad, which develops the theme that new beginnings are always possible.