The apostle Paul partially quoted Isaiah 52:7 here. The historical context of that verse is the deliverance of Israel from the oppression of another country. Israel seemed to always be in a cycle of judgment. She would break her covenant with God, then God would bring the judgment described in the Covenant. This judgment often included bondage by a neighboring country. Then God would, in His mercy, allow a repentant Israel to victoriously drive the invaders from her land.
This victory message was joyfully carried by messengers to all the villages and cities of Israel. And it is these messengers of victory whose feet are called “beautiful” in this passage. But Paul used this verse to describe a messenger who carries a different message of victory: the gospel of Jesus Christ.
The context is broader and everlasting. Every person in the world is under the judgment of God because of sin. The oppression of this judgment should be clear to all of us. We are captives to sin, illness, death, and then the final judgment. Since we all have sinned (Romans 3:23), this will not turn out good unless we have heard and believed the victory message: the gospel of Jesus Christ.
The gospel is the good news about the victory won by Jesus Christ on behalf of all who, by faith, receive the benefits of His death, burial, and resurrection. He fought and won the everlasting victory over sin, death, and eternal judgment.