Unity among the people of Israel, the covenant people of the Lord, helps to spiritually subdue surrounding peoples in the world. Again, representative nations during Isaiah’s time were used as symbols for the future. The enemies of God, in the western world and in the eastern world, will be spiritually overrun by united Israel, the covenant people.
The people cannot accomplish the work of God by themselves. The Lord intervenes in miraculous ways to gather his people.
“Assyria” represents all nations from which the remnant of Israel will be gathered. The Lord will provide a way (a “highway”) to deliver his people, as in the day of the great Exodus, and he will provide a way for them to come back to him. Read Doctrine and Covenants 133:25–33.