The text imagines a city waiting for news of the battle--will it be good news or bad? How are things going? In the distance a runner appears, and the sentinels on the city walls see him coming. They hear the good news that God has proven victorious. They see God's return. All break forth in shouts of thanksgiving. Everything is beautiful, even the feet of the runners, because of this happy news.
This passage functions as a reprise of the similar scene in 40:9-11. There, too, Zion announced the coming of God to comfort God's people. In both cases, the "gospel" term is used in the Greek Septuagint translation of the text: euangelizomai--to evangelize, to preach good news. The gospel is not a theory or a doctrine or even a teaching; it is news: God is coming! As God promised to comfort the people in 40:1, now God has done so (52:9).
7 How beautiful upon the mountains
are the feet of the messenger who announces peace,
who brings good news,
who announces salvation,
who says to Zion, Your God reigns.
8 Listen! Your sentinels lift up their voices,
together they sing for joy;
for in plain sight they see
the return of the Lord to Zion.
9 Break forth together into singing,
you ruins of Jerusalem;
for the Lord has comforted his people,
he has redeemed Jerusalem.
10 The Lord has bared his holy arm
before the eyes of all the nations;
and all the ends of the earth shall see
the salvation of our God.
New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org