Now when a man has learned through the commandments to recognize his helplessness and is distressed about how he might satisfy the law—since the law must be fulfilled so that not a jot or tittle shall be lost, otherwise man will be condemned without hope—then, being truly humbled and reduced to nothing in his own eyes, he finds in himself nothing whereby he may be justified or saved. Here the second part of Scripture comes to our aid, namely, the promises of God which declare the glory of God, saying, “If you wish to fulfill the law and not covet, as the law commands, come, believe in Christ in whom grace, righteousness, peace, liberty, and all things are promised you. If you believe, you shall have all things; if you do not believe, you shall lack all things.” That which is impossible for you to accomplish by trying to fulfill all the works of the law—many and useless as they all are—you will accomplish quickly and easily through faith.
It is clear that the justification which is unto eternal life Paul regards as consisting in our being constituted righteous, in receiving righteousness as a free gift, and this righteousness is none other than the righteousness of the one man Jesus Christ; it is the righteousness of his obedience. . . . Justification is thereby a constitutive act whereby the righteousness of Christ is imputed to our account and we are accordingly accepted as righteous in God’s sight.
– John Murray, Redemption Accomplished and Applied
The specific quality of faith is that it receives and rests upon another, in this case Christ and his righteousness.
– Murray, Ibid.