The phrase "come through" is repeated to show urgency that the people of Jerusalem must go outside the gates of the city to welcome foreigners or exiles coming back to the land of Israel. This is the most likely of several interpretations.
The word "build" is repeated to emphasize that God wants the road prepared well and level, perhaps quickly, so the people can come to him easily. See [Isaiah 57:14](../57/14.md).
## Raise up a signal flag for the nations ##
This means God is calling the people of the other nations to come to the land of Israel, to bring the exiles back, and to see what God has accomplished as he said he would.