From George Williams Believer's Bible Commentary
God having tested both the Hebrew and the Gentile nations, and both having broken down under the test, He shut them up in unbelief so that, being manifestly without merit, and having by demonstration forfeited all claims and all rights to divine favor, He might, in the unsearchable riches of His grace, have mercy upon them all.
(Believer's Bible Commentary. Nashville: Thomas Nelson)
The point of the verse is God's mercy upon all mankind and the magnitude of God's wisdom is revealed in the verse following verse 32:
Romans 11:32-33 For God hath concluded them all in unbelief, that he might have mercy upon all. O the depth of the riches both of the wisdom and knowledge of God! how unsearchable are his judgments, and his ways past finding out!
... conflating what is written in Romans 11 with what is written in Romans 9 is not proper interpretation of Scripture.
Here is the conclusion of what is written in Romans 9:
Romans 9:30-33
30 What shall we say then? That the Gentiles, which followed not after righteousness, have attained to righteousness, even the righteousness which is of faith.
31 But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.
32 Wherefore? Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumblingstone;
33 As it is written, Behold, I lay in Sion a stumblingstone and rock of offence: and whosoever believeth on him shall not be ashamed.
vs 30 – gentiles have attained to righteousness which is of faith.
vs 31-32 – Israel has not attained to righteousness because they sought it not by faith and, therefore, stumbled at the Stumblingstone.
vs 33 – whosoever believeth on the Stumblingstone shall not be ashamed (disappointed).
Here is the conclusion of what is written in Romans 11:
Romans 11:
32 For God hath concluded them all in unbelief, that he might have mercy upon all.
33 O the depth of the riches both of the wisdom and knowledge of God! how unsearchable are his judgments, and his ways past finding out!
34 For who hath known the mind of the Lord? or who hath been his counsellor?
35 Or who hath first given to him, and it shall be recompensed unto him again?
36 For of him, and through him, and to him, are all things: to whom be glory for ever. Amen.
vs 32 – reveals God's mercy upon all mankind.
vs 33 – the wisdom and knowledge of God are beyond the scope of the comprehension of mankind.
vs 34-35 – rhetorical statements as no one can know the mind of the Lord ... we can only know what He reveals to us concerning His thoughts. No one advised God ... no one can out-give God for God recompences over and above anything we give.
vs 36 – all things are of Him, and through Him, and to Him and He alone is worthy of all glory for ever.
From Vine's Expository Dictionary:
... He "gave Himself a ransom for all," indicating that the "ransom" was provisionally universal, while being of a vicarious character. Thus the three passages consistently show that while the provision was universal, for Christ died for all men, yet it is actual for those only who accept God's conditions, and who are described in the Gospel statements as "the many."
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