what's the relevance of lady macduff's speech (act 4 scene 2, 72-78) to the play and our society today?

L. Macduff's speech is relevant to the one of the going themes of the play. THe line numbers vary from book to book. I think you are referring to L. Macduff lamenting about where she should run to. She comments how evil deeds are rewarded in our world and good is punished. If you think about our world, this is much the same. This is a reason why Shakespeare's themes are timeless.