Father Abraham [Romans 4, TNIV]
It was not through the law that Abraham and his offspring received the promise that he would be heir of the world, but through the righteousness that comes by faith. For if those who depend on the law are heirs, faith means nothing and the promise is worthless, because the law brings wrath. And where there is no law there is no transgression. Therefore, the promise comes by faith, so that it may be by grace and may be guaranteed to all Abraham's offspring--not only to those who are of the law but also to those who have the faith of Abraham. He is the father of us all.
Paul wrote the letter to the Romans to explain to the Roman Christians that the righteous will live by faith and not by the law. To prove his point, he brought in the testimony of Abraham, the father of the Jews, to demonstrate his point. Abraham was not justified by the law, but by faith according to the Old Testament. If you have come to faith in Jesus through grace, you are a child of Abraham and a child of the promise of God! But the rest of Paul's story is that once you have been justified by faith, you need to live by faith and not the law. May you obey God today, not by trying harder to live by the law, but by resting more in Him and His amazing grace.