Paul, in his conclusion of this chapter, says (vv. 30-33):
What then shall we say? That the Gentiles, who did not pursue righteousness, have obtained it, a righteousness that is by faith; but the people of Israel, who pursued the law as the way of righteousness, have not attained their goal. Why not? Because they pursued it not by faith but as if it were by works. They stumbled over the stumbling stone. As it is written: “See, I lay in Zion a stone that causes people to stumble and a rock that makes them fall, and the one who believes in him will never be put to shame."
Since some Jews did obtain righteousness through faith, Paul is not talking about individuals but about Israel and the Gentiles in a general sense - God would now work through the Gentiles (in general) rather than Israel.
Paul's argument in chp 9 is that
God's cutting off Israel because of unbelief is not inconsistent with his clearly stated purpose in his word (9:6).
Following Paul's statement that nothing "will be able to
separate us from the love of God that is in Christ Jesus our Lord," he addresses the obvious question it raises: But what about Israel, they are cut off, separated from the love of God in Christ Jesus? Why does Israel not believe and receive sonship (see Jn 5:3-47)?
Paul first expresses his grief that Israel has been cut off, after being chosen as God's people (see Zec 11:4-11, where the reason for the judgment on Israel is given in vv. 1-3; viz, rejection of the Messianic Shepherd-King).
He points out that, although Israel was given many advantages by God, his
promise of sonship was not to all the descendants of Abraham,
just as
it was not to Ishmael and Esau.
God sovereignly chose Jacob to
inherit the promise instead of Esau,
before they were even born or
had done anything good or bad--
in order that his purpose in
election might stand; i.e., not by works but
by him who calls.
The issue Paul is preparing to address here is sonship by works, or by faith.
So having introduced God's sovereignty into his presentation, Paul addresses the obvious question it raises: So is God unjust to Esau, and Israel? His answer: Not at all, God has the right to dispense his mercy and compassion as he chooses, for it is not
owed to anyone, it is a gift, which has nothing to do with the recipient, but with God's soverign choice of to whom he will grant them.
To demonstrate the fact of God's
right to dispense, or not to dispense, mercy, Paul shows it is revealed in the name of God in the OT (Ex 33:19), and he shows its application in the account of Pharoah, concluding from both that God has mercy on whom he wants (chooses) to have mercy, and he hardens whom he wants (chooses) to harden.
Which then raises the next obvious question: Then why does he blame us for hardening our hearts? Who can resist his will that they be hardened?
Paul's answer. . .the sovereignty of God. "Who are you, O man, to talk back to God?" God is the sovereign potter who has the right to make from his clay some vessels for noble purposes and some for common use (human waste vessels for wrath).
Which raises the next issue: So why would he choose to make some vessels the objects of his wrath, who prepared
themselves for destruction, rather than make all vessels for mercy? His answer: what if God did this to make his wrath and power known, as a foil for making known to the objects of his mercy the riches of his glory (goodness). However, while no one can call God to account for what he does, Paul does point out God's great patience toward the objects of his wrath, for the purpose of bringing about the repentance of some.
Continuing on with his presentation of the sovereignty of God in election to mercy, Paul uses the prophecies of Hosea 2:23, 1:10 to show that the forgiving, saving, restoring God takes the Gentiles who are "not my people" and makes them "my people" by sovereignly grafting them
into the covenant.
Then he uses the prophecies of Is 10:22-23, 1:9 to show that only a small remnant of Israel would ever be
saved (see Ro 11:5-6), and that
God's calling includes both Gentiles and Jews,
but the great majority are Gentiles.
And we
know what the calling to both Jews and Gentles in the NT is:
to salvation,
through faith in Jesus Christ,
by grace.
Having introduced Gentiles into his presentation, he addresses
the reason for Israel's rejection and the Gentiles' calling:
unbelief and belief,
respectively. The
Gentiles pursued righteousness by faith and obtained it, while
Israel pursued it by works and did not attain it.
They stumbled over the Messiah,
the "
stumbling stone" (1Pe 2:8),
and fell into rejection.
Their u
nbelief and belief regarding what? Regarding rightousness, not by works but by faith in Jesus Christ, which is salvation.
That is the argument of Ro 9:
God's rejection of unbelieving Israel is not inconsistent with his promise they would be his people (
spiritual sonship),
because his promise was not to all, only to some, just as it was not to all Abraham's descendants, and he has saved and is saving some of them through faith in Jesus Christ.
So God's choice to work through either the Jews or Gentiles in a general sense
is necessarily a choice to salvation, because he works only through the saved
to spread the gospel of the kingdom.