How are the Gentiles included through the promises made to Abraham, Isaac, and Jacob?

Gentiles are included through the promises made to Abraham, Isaac, and Jacob because God's mercy and grace extend those covenants beyond Israel to the Gentiles, so that Gentiles might glorify God for His mercy. This inclusion was seeded in the Old Testament and realized when Paul goes to the Gentiles after Israel's rejection.

Les explains that God promised Abraham a nation, a land, and that He Himself in the Son would come as Messiah, King, and Redeemer. He came first to Israel to confirm the promises and covenants made to the fathers—Abraham, Isaac, and Jacob. After Israel's rejection, climaxing in Stephen's stoning, Paul goes to the Gentiles. Ephesians 1.2a shows Gentiles, even through promises made to the fathers, might glorify God for His mercy. Les says he now understands the mercy and grace of God.

Romans 15:9

And that the Gentiles might glorify God for his mercy; as it is written, For this cause I will confess to thee among the Gentiles, and sing unto thy name.

How do the Gentiles come to glorify God for His mercy?

Gentiles glorify God for His mercy through the promises made to the fathers—Abraham, Isaac, and Jacob. As verse 9 declares, it is by those promises that the Gentiles might glorify God for His mercy, showing that God's mercy and grace extend beyond Israel to include them.