The title for the cycle God's Great Supper comes from the book of Revelation Chapter 19 Verse 17. Revelation is a book in the New Testament. And not just any book, it is the final book of the bible. It is the retelling of a vision that John had (the same John who was a disciple of Jesus and who penned the Gospel of John). Interesting that it is the recounting of a vision and that its content recurs in Jed's dreams in the play.
Here is the section of Revelation 19 (with verse numbers included) referring to God's Great Supper:
11 I saw heaven standing open and there before me was a white horse, whose rider is called Faithful and True. With justice he judges and makes war. 12 His eyes are like blazing fire, and on his head are many crowns. He has a name written on him that no one knows but he himself. 13 He is dressed in a robe dipped in blood, and his name is the Word of God. 14 The armies of heaven were following him, riding on white horses and dressed in fine linen, white and clean. 15 Out of his mouth comes a sharp sword with which to strike down the nations. "He will rule them with an iron scepter."[a] He treads the winepress of the fury of the wrath of God Almighty. 16 On his robe and on his thigh he has this name written: KING OF KINGS AND LORD OF LORDS.
17 And I saw an angel standing in the sun, who cried in a loud voice to all the birds flying in midair, "Come, gather together for the great supper of God, 18 so that you may eat the flesh of kings, generals, and mighty men, of horses and their riders, and the flesh of all people, free and slave, small and great."
19 Then I saw the beast and the kings of the earth and their armies gathered together to make war against the rider on the horse and his army. 20 But the beast was captured, and with him the false prophet who had performed the miraculous signs on his behalf. With these signs he had deluded those who had received the mark of the beast and worshiped his image. The two of them were thrown alive into the fiery lake of burning sulfur. 21 The rest of them were killed with the sword that came out of the mouth of the rider on the horse, and all the birds gorged themselves on their flesh.