Why should Gentiles be considered part of God's people?

The inclusion of Gentiles as part of God's people is a central theme in Paul's writings, particularly in Ephesians 2:19-20 where he declares that Gentiles are no longer strangers but fellow citizens with saints. This transition is due to Christ's work on the cross, which reconciled all believers to God and to one another. It underscores the transformative nature of the Gospel—outside of it, Gentiles had no claim to God's promises, yet through faith in Christ, they are brought into the fold as children of God, ensuring that God’s mercy is extended to all nations.