I'm thankful that Jesus fulfilled the law... without it, he wouldn't be declared righteous by it, and wouldn't have been able to redeem me by giving up his righteousness (to Abraham) so that I might inherit it as an adopted descendant of Abraham... one with the same faith in the gospel of Jesus Christ that Abraham had:
[Gen 17:4-7 NASB] 4 "As for Me, behold, My covenant is with you, And you will be the father of a multitude of nations. 5 "No longer shall your name be called Abram, But your name shall be Abraham; For I have made you the father of a multitude of nations. 6 "I will make you exceedingly fruitful, and I will make nations of you, and kings will come forth from you. 7 "I will establish My covenant between Me and you and your descendants after you throughout their generations for an everlasting covenant, to be God to you and to your descendants after you.
[Rom 4:9-13, 16-17 NASB] 9 Is this blessing then on the circumcised, or on the uncircumcised also? For we say, "FAITH WAS CREDITED TO ABRAHAM AS RIGHTEOUSNESS." 10 How then was it credited? While he was circumcised, or uncircumcised? Not while circumcised, but while uncircumcised; 11 and he received the sign of circumcision, a seal of the righteousness of the faith which he had while uncircumcised, so that he might be the father of all who believe without being circumcised, that righteousness might be credited to them, 12 and the father of circumcision to those who not only are of the circumcision, but who also follow in the steps of the faith of our father Abraham which he had while uncircumcised. 13 For the promise to Abraham or to his descendants that he would be heir of the world was not through the Law, but through the righteousness of faith. ... 16 For this reason [it is] by faith, in order that [it may be] in accordance with grace, so that the promise will be guaranteed to all the descendants, not only to those who are of the Law, but also to those who are of the faith of Abraham, who is the father of us all, 17 (as it is written, "A FATHER OF MANY NATIONS HAVE I MADE YOU") in the presence of Him whom he believed, [even] God, who gives life to the dead and calls into being that which does not exist.
But notice what it says in Rom 4:13 - the promise (about being heir of the world) was "
not through the righteousness of the law" but through the
righteousness of faith. We who have the same faith in the gospel that Abraham had (Gal 3:8, Rom 4:10, 12, 16) are adopted heirs of the righteousness given to Abraham. Therefore, the righteousness we have is not a righteousness of our own, not a righteousness of works. It is an inherited righteousness ... the righteousness of Christ which was given to Abraham and promised as an inheritance to all of Abraham's descendants.
Therefore, to perform works of The Law of Moses to obtain righteousness is to reject our inheritance and seek to establish our own righteousness on the basis of works, rather than faith.
[Rom 10:1, 3-11 NASB] 1 Brethren, my heart's desire and my prayer to God for them is for [their] salvation. ... 3 For not knowing about God's righteousness and seeking to establish their own, they did not subject themselves to the righteousness of God. 4 For Christ is the end of the law for righteousness to everyone who believes. 5 For Moses writes that the man who practices the righteousness which is based on law shall live by that righteousness. 6 But the righteousness based on faith speaks as follows: "DO NOT SAY IN YOUR HEART, 'WHO WILL ASCEND INTO HEAVEN?' (that is, to bring Christ down), 7 or 'WHO WILL DESCEND INTO THE ABYSS?' (that is, to bring Christ up from the dead)." 8 But what does it say? "THE WORD IS NEAR YOU, IN YOUR MOUTH AND IN YOUR HEART"--that is, the word of faith which we are preaching, 9 that if you confess with your mouth Jesus [as] Lord, and believe in your heart that God raised Him from the dead, you will be saved; 10 for with the heart a person believes, resulting in righteousness, and with the mouth he confesses, resulting in salvation. 11 For the Scripture says, "WHOEVER BELIEVES IN HIM WILL NOT BE DISAPPOINTED."