This poem is about fighting for life until your last breath. Thomas reinforces the idea that life is a right worth fighting for. He is speaking to his father as he is dying, asking him to keep fighting so that Thomas can cry either tears of joy or sorrow
Thomas, Dylan. "Do Not Go Gentle into That Good Night." Reading the World: Contemporary Literature from Around the Globe. Ed. Carol Francis. Logan, IA: Perfection Learning, 2012. eBook.