Paul repeatedly describes our salvation as the imputation to us of “the righteousness of God”:
Rom 3:22 Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference:
Php 3:9 And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith:
And he also emphasizes that this righteousness is embodied in a Person, the Lord Jesus:
1Co 1:30 But of him are ye in Christ Jesus, who of God is made unto us wisdom, and righteousness, and sanctification, and redemption:
2Co 5:21 For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him.
This linkage of God’s righteousness with the salvation of his people is deeply rooted in the OT.
Psa 40:10 I have not hid thy righteousness within my heart;
I have declared thy faithfulness and thy salvation:
Psa 71:15 My mouth shall shew forth thy righteousness and thy salvation all the day;
Psa 98:2 The LORD hath made known his salvation:
his righteousness hath he openly shewed in the sight of the heathen.
Psa. 119:123 Mine eyes fail for thy salvation,
and for the word of thy righteousness.
Isa 46:13 I bring near my righteousness; it shall not be far off,
and my salvation shall not tarry:
Isa 51:4 Hearken unto me, my people; and give ear unto me, O my nation:
for a law shall proceed from me, and I will make my judgment to rest for a light of the people.
5 My righteousness is near; my salvation is gone forth, and mine arms shall judge the people;
the isles shall wait upon me, and on mine arm shall they trust.
6 Lift up your eyes to the heavens, and look upon the earth beneath:
for the heavens shall vanish away like smoke, and the earth shall wax old like a garment, and they that dwell therein shall die in like manner:
but my salvation shall be for ever,
and my righteousness shall not be abolished.
7 Hearken unto me, ye that know righteousness, the people in whose heart is my law;
fear ye not the reproach of men, neither be ye afraid of their revilings.
8 For the moth shall eat them up like a garment, and the worm shall eat them like wool:
but my righteousness shall be for ever, and my salvation from generation to generation.
Isa 56:1 my salvation is near to come, and my righteousness to be revealed.
And in fact Jeremiah twice announces the remarkable name, “the Lord our righteousness”:
Jer 23:6 In his days Judah shall be saved, and Israel shall dwell safely: and this is his name whereby he shall be called, THE LORD OUR RIGHTEOUSNESS. [cf. 33:16]
This statement closely anticipates Paul’s assertion that the Lord Jesus himself is the righteousness by which we “dwell safely” in the presence of a holy God.
In other words, what saves God’s people, according to the widespread testimony of the OT, is the righteousness of God.
This claim could be understood simply to mean that because God is righteous, he keeps his ancient promises to send a deliverer for his people. This is a true statement. But this idea is more naturally expressed by associating salvation with his lovingkindness חסד (xesed H2617, that is, his loyal love) or his faithfulness אמונה (emunah H530), and the OT is perfectly capable of saying this, in so many words:
2Sam. 22:51 He is the tower of salvation for his king:
and sheweth mercy xesed to his anointed,
unto David, and to his seed for evermore.
Is. 33:6 And wisdom and knowledge shall be the stability emunah of thy times,
and strength of salvation:
the fear of the LORD is his treasure.
Psa. 13:5 But I have trusted in thy mercy xesed; my heart shall rejoice in thy salvation.
Psa. 69:13 But as for me, my prayer is unto thee, O LORD, in an acceptable time:
O God, in the multitude of thy mercy xesed hear me, in the truth of thy salvation.
Psa. 85:7 Shew us thy mercy xesed, O LORD, and grant us thy salvation.
Psa. 98:3 He hath remembered his mercy xesed and his truth emunah toward the house of Israel:
all the ends of the earth have seen the salvation of our God.
Psa. 119:41 Let thy mercies xesed come also unto me, O LORD, even thy salvation, according to thy word.
How has God carried out his loyal love and his faithfulness in saving his people? The OT and NT agree that he does so by giving us his own righteousness. Psalm 40 combines all of these concepts, God’s righteousness, his faithfulness, and his loyal love, combining to bring us salvation:
Psa. 40:10 I have not hid thy righteousness within my heart; I have declared thy faithfulness emunah and thy salvation: I have not concealed thy lovingkindness xesed and thy truth from the great congregation.
Jeremiah may have pondered just how the Lord himself could be our righteousness, but he faithfully asserted what the Spirit of Christ revealed to him, and Paul shows us how God has done this, by sending his Son to execute the complete transaction, taking our sin upon himself and clothing us with his perfect obedience. Thus we are “accepted in the Beloved” (Eph 1:6).