“But now the righteousness of God has been manifested apart from the law, although the Law and the Prophets bear witness to it— the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction:” -Romans 3:21–22
Since the law requires perfect and absolute obedience, and not one has been found to have been so obedience, to have attained the required perfect measure of holiness, then it follows all have fallen short—Gentile and Jew alike. There is not distinction between the two on these grounds.
The righteousness that God requires of all men must then issue from himself and be manifest to us in the Son, Jesus Christ, who is alone just. Through the instrument of faith (which is also a gift God gives to us Cf. Ephesians 2:8-10), this righteousness is transferred to those of us who believe.
John Calvin notes, “Ut ergo justificemur, causa efficiens est misericordia Dei, Christus materia, verbum cum fide instrumentum.”
[When therefore we are justified, the efficient cause is the mercy of God, the meritorious is Christ, the instrumental is the word in connection with faith.]
This is why the Reformers would say we are justified by faith alone (Sola Fide). They didn’t mean faith exclusively as to exclude Christ alone, etc. They mean faith alone (not our works according to the Law) is the instrument by which we receive Christ, in whom righteousness is conveyed to us.