6 But it is not that the word of God has taken no effect. For they are not all Israel who are of Israel,
Romans 9 to 11 show that God’s choice of those who will be saved is based on the principle of grace through faith and that He has a regenerate remnant chosen by grace:
Ro 11:6, And if by grace, then it is no longer of works; otherwise grace is no longer grace. But if it is of works, it is no longer grace; otherwise work is no longer work.
Verses 6 to 13 are a theodicy (defense of God’s character) showing that God is righteous in dealing with the nation Israel. God’s promises can only be realized by those who have Abraham’s faith. Paul demonstrated ethnic Israel’s rejection of the gospel by showing Isaac accepted God’s promise by faith, whereas Ishmael did not (9:6-9).
There is no injustice on God’s part (vv. 14-24) because of His mercy. That mercy may be extended to Gentiles as well (vv. 25-33). Therefore, if God’s covenant is not applied by an individual, that does not mean that God is unfaithful (10:1-21).
6 But it is not that the word of God has taken no effect.
Israel’s rejection of the Messiah did not mean that the Word of God failed. God kept His word that people will be saved through accepting His promise (Ge. 15:6). Paul did not want people to think, because he suffered sorrow over Israel’s unbelief, that the Word of God was not effective. Nowhere has God abrogated His Word. His promises stand because of this. He is justified in all that He does.
Paul went on to show that God has not failed His promise using a series of quotations from the Old Testament (vv. 7, 9, 12, 13, 15, 17, 20, 25-29). This is documentation to show that He is always true to Himself and others.
For they are not all Israel [ethnic Israel] who are of [descendants of] Israel [believing Israel],
Not every Israelite is a regenerate Israelite. There are three different kinds of Israelites (Ro 2:28-29):
1. Racial—physical Israelites
2. Religious—believed in the Old Testament but not the New Testament
3. Regenerate—believe that Jesus Christ is the Messiah
There is not just one Israel but two: one regenerate and the other unregenerate. If we understand verse 6, we will comprehend verses 7 through 14. God always justly honors the free will of the human being.
This verse deals with two kinds of Israelites: racial and regenerate. National heritage is not the same as spiritual standing. Many Israelites were simply physical Jews, others were religious but not regenerate. God places no priority on race, nationalism, or ethnicity when it comes to salvation. God did not reject Israel, He simply chooses to save those who believe in Him by faith. There is indeed a true, regenerate Israel.
National Israel exists because of God’s sovereignty in choosing Abraham, Isaac, and Jacob. Through this election He would fulfill His purpose in choosing a theocratic nation.
Romans chapters 9 to 11 nowhere states that “Israel” is the church. The issue in this section has to do with whether the promises made to the theocratic nation apply to all ethnic Israel. To the contrary, verses 7 to 13 argue that God winnows true Israel from ethnic Israel because He always operates on His justice.
The “word” in verse six that had not failed in the first phrase was His promise. Not everyone in Israel believed the promise. The reason God’s Word has not failed is that there are two Israels. There is a smaller group of believing Jews to which we refer as “the remnant.”
God’s promise always operates justly.
God’s Word did not fail, because salvation is not a physical issue but a spiritual issue. People must come to God by faith, not works. God’s promise did not automatically apply to those born as physical Israelites. As God chose Isaac rather than Ishmael by promise, so He chooses those who come to Him by grace through faith.
Ro 4:16, Therefore it is of faith that it might be according to grace, so that the promise might be sure to all the seed, not only to those who are of the law, but also to those who are of the faith of Abraham, who is the father of us all
In my KJV bible, Chapter 16:3-16, it states that Hagar was the mother of Ishmael.