Answer
Students of literature will know that it is an artistic way of saying that the Scripture (in fact God through Scripture) speaks about the righteousness of faith.
It is one of the literary devices used by the writers.
“It” is the Scripture.
Explanation
The context is given by Paul in Romans 9:31-32.
“but Israel following after a Law of righteousness did not arrive
at a Law of righteousness? Why? Because it was not of faith,
but as of works of Law. For they stumbled at the
Stone-of-stumbling”.
Israel (Jew first and then the Greeks/Gentiles) was supposed to reach at the law (standard) of righteousness.
It was to be done through “faith” in the sacrifice of Jesus Christ.
But the Jews tried to reach it through the “works of law” (animal sacrifices).
Thus we learn that:
The best example one can cite to explain the controversy of “law vs. faith” is Apostle Paul himself.
Before conversion, he was far from the Law of righteousness:
“the one who before was a blasphemer, and a persecutor, and
insolent” (1 Tim 1:13).
But as a Jew he was perfect in his Jewish life following the works of Law:
“If any other thinks that he has reason to trust in the flesh, I
more. I was circumcised the eighth day, of the stock of Israel, of the
tribe of Benjamin, a Hebrew of the Hebrews. As regards the Law, I
was a Pharisee; concerning zeal, persecuting the church; regarding
the righteousness in the Law, blameless” (Phlp 3:4-6).
Paul before his conversion, as a “blasphemer”, “persecutor” and “insolent” cannot be talking about the spiritual Law. He is talking about the Works of Law because the original Law doesn’t talk anything about Pharisee.
Paul is talking about a different law here, the ritual law with traditions added by the fathers:
“I am truly a man, a Jew born in Tarsus in Cilicia, yet brought up in
this city at the feet of Gamaliel, taught according to the exactness
of the Law of the fathers, being a zealous one of God, as you all
are today. I persecuted this Way as far as death, binding and
delivering both men and women into prisons” (Acts 22:3-4).
At that stage Paul could never reach the Law of righteousness even if he fervently tried. Why?
“And so people become enemies of God when they are controlled by their
human nature; for they do not obey God's law, and in fact they
cannot obey it” (Rom 8:7).
Yet, one day, because of God’s grace, he received mercy. He was made righteous by God.
“but I received mercy, because being ignorant I did it in
unbelief” (1 Tim 1:13).
Paul didn’t deserve this because he was a blasphemer, persecutor and insolent. Yet God showed mercy through His grace and Paul was given faith in a powerful way on the road to Damascus.
“But the grace of our Lord abounded exceedingly with faith and
love in Christ Jesus. Faithful is the Word and worthy of all
acceptance, that Christ Jesus came into the world to save sinners,
of whom I am chief. But for this reason I received mercy, that
in me first Jesus Christ might show forth all long-suffering, for an
example to those being about to believe on Him to everlasting life” (1
Tim 1:14-16).
Conclusion
Paul, earlier, as a Pharisaic Jew, thought that the traditions of his fathers with strict observances of animal sacrifices absolved him of his sins.
But he learned through faith that only Jesus’ unique sacrifice as the Lamb of God absolved his sins. Thus he was “made righteous” by God. Thereafter he did “good works” obeying God’s spiritual laws.
This is the righteousness which is of faith.
“Even as also David says of the blessedness of the man to whom God
counts righteousness apart from works: "Blessed are those whose
lawlessnesses are forgiven, and whose sins are covered” (Rom 4:6-7).