Abraham's faith was reckoned for righteousness because up until Jesus, the faith of Christ was not available...but now! Paul is using Abraham as an example of what we've got now simply by believing in God's word concerning Jesus Christ.
22 But the scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe.
23 But before faith came, Whose faith? Christ's faith we were kept under the law, shut up unto the faith which should afterwards be revealed. Whose faith was revealed? The faith of Jesus Christ!
24 Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith.
25 But after that faith is come, After whose faith is come? Christ's faith we are no longer under a schoolmaster.
The faith of Christ is available and present within all who become indwelt by the Holy Spirit because faith is given by the Holy Spirit, regardless of when they live. The receiving of the Holy Spirit alone is the source/cause of true faith.
[Psa 51:11 KJV] 11 Cast me not away from thy presence; and take not thy holy spirit from me
[Gal 3:5-6 KJV]
5 He therefore that ministereth to you the Spirit,
and worketh miracles among you, [doeth he it] by the works of the law, or by the hearing of faith?
6 Even as Abraham believed God
, and it was accounted to him for righteousness.
[1Pe 1:11 KJV]
11 Searching what, or what manner of time the Spirit of Christ which was in them
did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow.
The verses following, CLEARLY demonstrates that FAITH was RECKONED to Abraham FOR RIGHTEOUSNESS. How can that even be in dispute?
[Rom 4:9 KJV]
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.
[Rom 4:10 KJV]
10 How was it then reckoned?
when he was in circumcision, or in uncircumcision? Not in circumcision, but in uncircumcision.
[2Pe 1:1 KJV]
1 Simon Peter, a servant and an apostle of Jesus Christ, to them that have obtained like precious faith with us through the righteousness of God and our Saviour Jesus Christ:
2Ti 1:9-10 KJV] 9 Who hath saved us, and called [us] with an holy calling, not according to our works, but according to his own purpose and grace, which was given us in Christ Jesus before the world began,
Christ's faith is given individually to those who are to receive it at a time of God's choosing regardless of when they lived.
That faith is the faith being spoken of in "after that faith has come" - the faith that is given individually.
Christ's faith was/is of Him eternally and transcends time. One of Christ's names is "Faithful and True"
Christ being the author and finisher of faith.
[Gal 2:16 KJV]
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.