2 Samuel - Chapter 10

As well as the story of Jesus, the Old Testament is the story of the Jewish nation.  However, Gentiles appear in the story in unexpected ways.

In this Chapter David is at war with the Ammonites, and ends up with them subject to Israel.

In Matthew Chapter 1 we have the Genealogy of Jesus, and in verse 7  we see Solomon, the father of Rehoboam, and Rehoboam the father of Abijah.  

And in 1 Kings 14  we read about Rehoboam:

"Rehoboam son of Solomon was king in Judah. He was forty-one years old when he became king, and he reigned seventeen years in Jerusalem, the city the Lord had chosen out of all the tribes of Israel in which to put his Name. His mother’s name was Naamah; she was an Ammonite."

The Ammonites may have been hostile to Israel, but they find themselves in Jesus' Genealogy.  In this way we see that nobody is excluded from Jesus' salvation.