Randy receives a call from Western Union. Who is the telegram from and what does it say and mean?

Randy answers Florence's Western Union call. She informs him it's a cable from Mark. She reads the urgent message and Randy feels sick. Florence asks whether "Alas, Babylon" is from the Bible. Randy says he doesn't know but recognizes their family signal. "Alas, Babylon" is from Revelation and signifies impending doom. Mark and Randy agree the previous Christmas that "Alas, Babylon" signifies a potential nuclear confrontation with the Soviet Union.