The phrase In that day indicates that a new unit begins here (see the comments on Isa 27.1).

From the river Euphrates to the Brook of Egypt refers to the whole territory from Babylonia to Egypt. The river Euphrates flowed through Babylonia and Assyria (see 7.20), while the Brook of Egypt refers to the small river that formed the boundary between Egypt and Israel (see Num 34.5). The territory in view here is actually the widest geographical extent of Israel’s promised land (see Gen 15.18).

The LORD will thresh out the grain is a figure of speech. It pictures Yahweh separating his people from among the people where they were exiled like someone separating the good grain from the useless chaff. The grain and the chaff may refer to Israel and their foreign enemies respectively, or to faithful and unfaithful Israelites. For the activity of threshing, see the comments on 21.10. If this activity is unknown in a culture, translators may render this line as “The LORD will separate the grain from the chaff” or “… separate the good from the bad [fruit of the harvest].” Good News Translation uses a simile instead of a metaphor here for clarity.

And you will be gathered one by one, O people of Israel means Yahweh will gather the Israelites together again. The Hebrew verb rendered gathered refers to the act of “gleaning,” picking up what is left after the harvest (see the comments on 17.5). The phrase one by one emphasizes that the gleaning will be complete—not even one grain will be left behind. Yahweh will gather all his people. For languages that prefer to place the vocative O people of Israel at the beginning of the verse, see the second example below. Good News Translation changes the second person reference to Israel to third person as in the rest of the section. If translators adopt Good News Translation‘s model here for naturalness, they should add “Israel” by rendering this line as “and the LORD will gather his people of Israel one by one.”

Translation examples for this verse are:

• At that time Yahweh will separate the grain from the chaff, gathering you people of Israel one by one from the lands between the Euphrates River and the River of Egypt.

• O people of Israel, at that time Yahweh will separate the good from the bad, and gather you one by one from the Euphrates River to the River of Egypt.

Quoted with permission from Ogden, Graham S. and Sterk, Jan. A Handbook on Isaiah. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here .