Rejoice and be glad, daughter of Edom, that dwell in the land of Uz: The cup shall pass through to you also; you shall be drunken, and shall make yourself naked.
"Rejoice and be glad, O daughter of Edom"  (Lamentations 4:21a).  This is sarcasm.  It is as though he said, "Go ahead and laugh, O Edom, God will take care of you also, before it's all ended."