The text does not say that the Gentiles were foreknown by God. The Old Testament declares that the nation of Israel was those people that were foreknown, the descendants of Abraham, Isaac and Jacob.
Not the Gentiles, the Gentiles were foreign to the covenant that God established with Israel.
The Gentiles were uncircumcised, not under the law, God never inhabited any Gentile temple. The Gentiles were dogs, filthy sinners, the Gentiles never knew God. Jesus was not a Gentile and Jesus was sent only to the Jews.
Matthew 15:24
But He answered and said, “
I was sent only to the lost sheep of the house of Israel.”You are missing the central point here. The Jews whom were foreknown by God were grafted out, and the Gentiles were later grafted into the olive tree.
Simply because the rejection of the Christ by the Jews increased the grace of God towards the Gentiles.
Romans 11:15
For if their rejection is the reconciliation of the world, what will their acceptance be but life from the dead?
The definition of Gentile means not chosen, non elect, not formerly known by God, not Jewish.
Gentiles were unnatural branches that had to be grafted in and the Jews, the natural cultivated branches were severed.
The Jews opposed God while under the law of God and that opposition amplified God's grace.
Romans 5:20
The Law came in so that the transgression would increase; but where sin increased, grace abounded all the more.
That amplification of grace became so great in the rejection of the Christ by the Jews. That grace swept outwards from Israel to the surrounding nations.
Israel is the subject of nearly the entire narration of the Old Testament.