How does the reappearance of Krogstad tie in with the changes on stage?

The stage has become a sight of the "evening ritual," a mother playing with her children and getting ready to send them off to bed......... she is of course doing what she's expected to do, and the arrival of Krogstad not only interferes with the ritual but surprises and startles Nora........... just appearing, it's simply not done or excepted.

With her husband gone, as well as her friend, Krogstad catches Nora unprotected. He probes her for information she doesn't have and when he figures out she doesn't have it urges her to use her feminine charms. He doesn't realize she does as she's told..... that it isn't her place to do the "telling." Krogstad wants her to gain information through seduction or possibly the removal of affection..... when her husband returns it doesn't take him long to figure out what's going on.