Paul continues this idea about the promises to Israel in relation to Faith, going all the way back to the days of Abraham, showing the establishing of God's promises through a chosen seed that would eventually include all peoples on that same Faith Abraham had...
Rom 4
4 What shall we say then that Abraham our father, as pertaining to the flesh, hath found?
Wait a minute. Did Paul just call Abraham "our father" there, like a patriarch father in Christ's Church? Keep going to find out.
2 For if Abraham were justified by works, he hath whereof to glory; but not before God.
3 For what saith the scripture? Abraham believed God, and it was counted unto him for righteousness.
If Abraham was justified by works, then he would have the right to claim his glory in that. But the Scripture (Genesis 15) says Abraham believed... God, and by that it was counted to Abraham as righteousness.
4 Now to him that worketh is the reward not reckoned of grace, but of debt.
The reward for doing a work creates a debut that is owed you. That's not grace, which grace is something freely given not earned by a work.
5 But to him that worketh not, but believeth on Him That justifieth the ungodly, his faith is counted for righteousness.
Through Faith by believing on Him That justifies the ungodly, that Faith is not of works and is not a debut, so that Faith is counted as righteousness.
6 Even as David also describeth the blessedness of the man, unto whom God imputeth righteousness without works,
7 Saying, 'Blessed are they whose iniquities are forgiven, and whose sins are covered.
8 Blessed is the man to whom the Lord will not impute sin.'
Those whom God does not impute sin, for we are all sinners, those are blessed because God has imputed to them righteousness without works. Now that's His Grace for our Faith on His Son Jesus Christ.
9 Cometh this blessedness then upon the circumcision only, or upon the uncircumcision also? for we say that faith was reckoned to Abraham for righteousness.
Was this being blessed state only for the circumcision, i.e., the seed of Israel, or also for the Gentiles?
10 How was it then reckoned? when he was in circumcision, or in uncircumcision? Not in circumcision, but in uncircumcision.
11 And he received the sign of circumcision, a seal of the righteousness of the faith which he had yet being uncircumcised: that he might be the father of all them that believe, though they be not circumcised; that righteousness might be imputed unto them also:
12 And the father of circumcision to them who are not of the circumcision only, but who also walk in the steps of that faith of our father Abraham, which he had being yet uncircumcised.
God imputed righteousness to Abraham for his Faith before... Abraham was circumcised in his flesh. The token of circumcision was given later, and not subject to this Promise by Faith offered Abraham at the first. Our Heavenly Father did this so that Abraham would be the father (spiritual father) of ALL of those who believe on Jesus Christ, even for the Gentile that is not flesh circumcised.
13 For the promise, that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith.
14 For if they which are of the law be heirs, faith is made void, and the promise made of none effect:
15 Because the law worketh wrath: for where no law is, there is no transgression.
Paul goes right to the nitty-gritty. God's Promise by Faith that Abraham should be heir of the world was not to Abraham or to his seed through the law, but by the righteousness of Faith. Does Paul show God's promises ended by that righteousness of Faith? God forbid no!
16 Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,
Again, Apostle Paul confirms that the Promise by Faith is to all the seed of Israel, and not only to them, but to all Gentiles too. (For that Promise to have affect, one must believe on Jesus Christ, but that does not affect that the promise is to ALL).
17 (As it is written, I have made thee a father of many nations,) before Him Whom he believed, even God, Who quickeneth the dead, and calleth those things which be not as though they were.
18 Who against hope believed in hope, that he might become the father of many nations; according to that which was spoken, So shall thy seed be.
Which "seed" is Paul pointing to in that? The seed of Israel? Not just Israel, but to all that believe on Jesus. So if the seed of Israel doesn't matter anymore in Christ like some infer, then why does Paul keep bringing them up here? It's because Paul well knew not all the promises God gave to the seed of Israel were fulfilled yet in his days. They still won't be until after Lord Jesus returns, so there's still a lot written in the OT prophets that is yet to be fulfilled today.
19 And being not weak in faith, he considered not his own body now dead, when he was about an hundred years old, neither yet the deadness of Sara's womb:
20 He staggered not at the promise of God through unbelief; but was strong in faith, giving glory to God;
21 And being fully persuaded that, what He had promised, he was able also to perform.
22 And therefore it was imputed to him for righteousness.
That was one of God's Promises to Abraham involved in Him imputing righteousness to Abraham. And Abraham didn't waiver, even though he was in his old age and didn't think to be able to have a child. Sarah especially laughed when The Angel of The LORD told her she would have a child in her old age. Yet Abraham believed God would do what He said, and God counted it to Abraham as righteousness.
23 Now it was not written for his sake alone, that it was imputed to him;
24 But for us also, to whom it shall be imputed, if we believe on Him That raised up Jesus our Lord from the dead;
25 Who was delivered for our offences, and was raised again for our justification.
KJV
If we also believe on The Father Who raised His Son Jesus Christ from the dead, and died on the cross for us, then that righteousness by Faith is also imputed to us, regardless if we are of the seed of Israel or of the Gentiles.
Yet still, that shows God's Promises to the seed are NOT... done away with in Christ Jesus. Gentiles will be in shock when Jesus comes and they find out how pretty much the majority of the 12 tribes of Israel had believed on Jesus Christ.