This verse explains why Jerusalem needs to expand, so it begins with the Hebrew particle ki rendered For.

You will spread abroad to the right and to the left is the first reason, stating that the city’s population will expand and spread throughout the land of Israel. Spread abroad could imply that they will go beyond their national borders. However, the Hebrew verb rendered spread abroad simply means “to spread out.” Revised Standard Version adds the word abroad, but the other versions consulted do not. The Hebrew verb here is also used in Gen 28.14, where it says Abraham and his descendants will spread throughout the land of Canaan. To the right and to the left means “everywhere” in the land (compare 9.20). This phrase may be rendered “in all directions.” Good News Translation and Bible en français courant have “on all sides.” For this whole line Revised English Bible says “you will spread from your confines right and left.” Good News Translation is similar with “You will extend your boundaries on all sides.” Jerusalem will have to expand in all directions to accommodate its growing population.

And your descendants will possess the nations could be understood to mean that the Israelites will conquer the world. However, this line means the people returning from exile in Babylonia will once again inhabit the whole land of Canaan. As in Deut 9.1 and 11.23, the phrase possess the nations refers to the Israelites taking possession of Canaan. They will retake it from the various tribal groups that now lived there. In this context the nations are probably the non-Israelite groups who had seized Israelite property when the owners were taken to Babylonia as exiles. By using these expressions, God seems to suggest that when the exiles return to their land they will repeat what their ancestors did when they first entered Canaan under Joshua. The verb possess is better rendered “dispossess” (New International Version, Revised English Bible, New Jerusalem Bible, New Jewish Publication Society’s Tanakh) or “drive out.” A good alternative for the nations is “the foreigners.” Good News Translation renders this whole line clearly with “your people will get back the land that the other nations now occupy.”

And will people the desolate cities completes the promise of reoccupying the land. The returning exiles will once again inhabit (people) the cities of Canaan that had been destroyed. The desolate cities refers to all the towns destroyed by the Babylonians when they invaded in 597-587 B.C. The Hebrew word for desolate means “abandoned” or “deserted” (see the comments on 49.8). For this whole line Good News Translation has “Cities now deserted will be filled with people.”

For the translation of this verse consider the following examples:

• For you will spread far in all directions,
and your descendants [or, people] will drive out the other peoples,
and repossess the cities that have been destroyed.

• Because you will expand all around;
your descendants will dispossess the foreigners,
and once again inhabit the cities that were deserted.

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 .