On the twenty-first Sunday in Ordinary Time, the first reading is from the Book of the Prophet Isaiah 66:18-21. Isaiah 66 is considered part of Third Isaiah. It was written as a prophetic book following the Babylonian exile. The tone of this reading is apocalyptic. It looks forward to the creation of a new heaven and a new earth. God gives the nation the role of bringing back to Jerusalem “all your brothers and sisters” from the lands where they have been scattered. An essential purpose of the gathering of Israel and the nations is thus worship. The final verse of this reading seems to describe an extraordinary transformation.