In fact, after Israel was concluded having continued in said Unbelief, God used that aspect of their Abrahamic Covenant to show through a Gentile (Cornelius) that Israel (through God's interruption of Peter's words to him), that God had concluded to Unbelieving Israel "under sin" or "sinners of the Gentiles."
At which point He was THEN no longer respecting (going by) whether one was a Jew or a Gentile.
What you are doing is reading later, no distinction status, into that earlier, Israel First and go through Israel, status.
That changed after this...
Acts 7:51 Ye stiffnecked and uncircumcised in heart and ears, ye do always resist the Holy Ghost: as your fathers did, so do ye. 7:52 Which of the prophets have not your fathers persecuted? and they have slain them which shewed before of the coming of the Just One; of whom ye have been now the betrayers and murderers: 7:53 Who have received the law by the disposition of angels, and have not kept it.
Notice how that the following ends in the same way as that...
Romans 2:17 Behold, thou art called a Jew, and restest in the law, and makest thy boast of God, 2:18 And knowest his will, and approvest the things that are more excellent, being instructed out of the law; 2:19 And art confident that thou thyself art a guide of the blind, a light of them which are in darkness, 2:20 An instructor of the foolish, a teacher of babes, which hast the form of knowledge and of the truth in the law. 2:21 Thou therefore which teachest another, teachest thou not thyself? thou that preachest a man should not steal, dost thou steal? 2:22 Thou that sayest a man should not commit adultery, dost thou commit adultery? thou that abhorrest idols, dost thou commit sacrilege? 2:23 Thou that makest thy boast of the law, through breaking the law dishonourest thou God? 2:24 For the name of God is blasphemed among the Gentiles through you, as it is written. 2:25 For circumcision verily profiteth, if thou keep the law: but if thou be a breaker of the law, thy circumcision is made uncircumcision.
Notice what that leads to...
Romans 3:9 What then? are we better than they? No, in no wise: for we have before proved both Jews and Gentiles, that they are all under sin;
Which was what this was about...
Acts 10:9 On the morrow, as they went on their journey, and drew nigh unto the city, Peter went up upon the housetop to pray about the sixth hour: 10:10 And he became very hungry, and would have eaten: but while they made ready, he fell into a trance, 10:11 And saw heaven opened, and a certain vessel descending unto him, as it had been a great sheet knit at the four corners, and let down to the earth: 10:12 Wherein were all manner of fourfooted beasts of the earth, and wild beasts, and creeping things, and fowls of the air. 10:13 And there came a voice to him, Rise, Peter; kill, and eat. 10:14 But Peter said, Not so, Lord; for I have never eaten any thing that is common or unclean. 10:15 And the voice spake unto him again the second time, What God hath cleansed, that call not thou common.
10:28 And he said unto them, Ye know how that it is an unlawful thing for a man that is a Jew to keep company, or come unto one of another nation; but God hath shewed me that I should not call any man common or unclean.
In other words, God had concluded both were now on an equal footing as to access to Him now...
The very principle Paul later reminded Peter of having dissed...
Galatians 2:14 But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews? 2:15 We who are Jews by nature, and not sinners of the Gentiles, 2:16 Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified. 2:17 But if, while we seek to be justified by Christ, we ourselves also are found sinners, is therefore Christ the minister of sin? God forbid.
Which takes that back to where Romans 3 leaves off AFTER God has concluded both "under sin..."
Romans 3:27 Where is boasting then? It is excluded. By what law? of works? Nay: but by the law of faith. 3:28 Therefore we conclude that a man is justified by faith without the deeds of the law. 3:29 Is he the God of the Jews only? is he not also of the Gentiles? Yes, of the Gentiles also: 3:30 Seeing it is one God, which shall justify the circumcision by faith, and uncircumcision through faith. 3:31 Do we then make void the law through faith? God forbid: yea, we establish the law.
Should any of this throw you, just reread it a few times - these things wind in and out throughout their whole narrative.
Suffice it to say that AFTER Unbelieving Israel was concluded "under sin" with the Gentiles, per this...
Romans 3:19 NOW WE KNOW that what things soever the law saith, it saith to them who are under the law: that every mouth may be stopped, and all the world may become guilty before God. 3:20 Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.
This THEN came into effect...
Romans 3:21 BUT NOW the righteousness of God WITHOUT the law is manifested, being witnessed by the law and the prophets; 3:22 Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference: 3:23 For all have sinned, and come short of the glory of God; 3:24 Being justified freely by his grace through the redemption that is in Christ Jesus: 3:25 Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God; 3:26 To declare, I say, at this time his righteousness: that he might be just, and the justifier of him which believeth in Jesus.