Galatians 3:15-18 (NASB) 15 Brethren, I speak in terms of human relations: even though it is only a man's covenant, yet when it has been ratified, no one sets it aside or adds conditions to it. 16 Now the promises were spoken to Abraham and to his seed. He does not say, "And to seeds," as referring to many, but rather to one, "And to your seed," that is, Christ. 17 What I am saying is this: the Law, which came four hundred and thirty years later, does not invalidate a covenant previously ratified by God, so as to nullify the promise. 18 For if the inheritance is based on law, it is no longer based on a promise; but God has granted it to Abraham by means of a promise.
it should be pretty obvious...
The covenant of faith exists apart from the law, but the law does not exist apart from the covenant of faith.
the covenant of faith made with Abraham 430 years before the law was given was ratified in the latter half of Genesis 15.
Romans 3:21-22 (NASB) 21 But now apart from the Law the righteousness of God has been manifested, being witnessed by the Law and the Prophets, 22 even the righteousness of God through faith in Jesus Christ for all those who believe; for there is no distinction;
So the law is a witness to the covenant of faith, but didn’t add any conditions to the covenant of faith.
The purpose of the law was to legally establish Christ’s innocence & sinlessness brining righteousness into the fallen creation. It is Christ’s righteousness which was exchanged/redeemed and given to Abraham so that it could be the inheritance to all of Abraham’s descendants.
our faith doesn’t qualify us for righteousness... it qualifies us as descendants of Abraham... and descendants of Abraham inherit Christ’s righteousness.
Galatians 3:6-9 (NASB) 6 Even so Abraham BELIEVED GOD, AND IT WAS RECKONED TO HIM AS RIGHTEOUSNESS. 7 Therefore, be sure that it is those who are of faith who are sons of Abraham. 8 The Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand to Abraham, saying, "ALL THE NATIONS WILL BE BLESSED IN YOU." 9 So then those who are of faith are blessed with Abraham, the believer.
18 For if the inheritance is based on law, it is no longer based on a promise; but God has granted it to Abraham by means of a promise.
26 For you are all sons of God through faith in Christ Jesus.
29 And if you belong to Christ, then you are Abraham's descendants, heirs according to promise.
Galatians 4:21-31 (NASB) 21 Tell me, you who want to be under law, do you not listen to the law? 22 For it is written that Abraham had two sons, one by the bondwoman and one by the free woman. 23 But the son by the bondwoman was born according to the flesh, and the son by the free woman through the promise. 24 This is allegorically speaking, for these women are two covenants: one proceeding from Mount Sinai bearing children who are to be slaves; she is Hagar. 25 Now this Hagar is Mount Sinai in Arabia and corresponds to the present Jerusalem, for she is in slavery with her children. 26 But the Jerusalem above is free; she is our mother. 27 For it is written, "REJOICE, BARREN WOMAN WHO DOES NOT BEAR; BREAK FORTH AND SHOUT, YOU WHO ARE NOT IN LABOR; FOR MORE NUMEROUS ARE THE CHILDREN OF THE DESOLATE THAN OF THE ONE WHO HAS A HUSBAND." 28 And you brethren, like Isaac, are children of promise. 29 But as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so it is now also. 30 But what does the Scripture say? "CAST OUT THE BONDWOMAN AND HER SON, FOR THE SON OF THE BONDWOMAN SHALL NOT BE AN HEIR WITH THE SON OF THE FREE WOMAN." 31 So then, brethren, we are not children of a bondwoman, but of the free woman.