13 For the promise that he would be the heir of the world was not to Abraham or to his seed through the law, but through the righteousness of faith.
Jews considered keeping the law as the basis for their standing with God. Paul turned to an argument that shows Abraham acted on the principle of faith, not law, for salvation. This is an advance on the argument that no one can obtain salvation by rite (such as circumcision in the previous verses).
13 For the promise that he [Abraham] would be the heir of the world
God never abrogated His unconditional promises to Abraham. This promise is not a conditional promise. Therefore, the promise rests upon God and not upon Abraham. There is a parallel between promise and grace. Under grace, God does the doing. This idea is inherent in promise as well.
God will ultimately fulfill all His unconditional promises in the Millennial kingdom—“heir of the world.” An “heir” is someone who receives possessions. Psalm 37 five times demonstrates that Israel will inherit the promised land (vv. 9, 11, 27, 29, 34). The Abrahamic Covenant promised Abraham that he would have physical progeny and a land that extends from the Euphrates to the river of Egypt (Ge 12-15; especially 15:18). This was an eschatological promise, but the central idea here is the covenant of promise from God’s viewpoint.
was not to Abraham or to his seed [offspring] through the [no definite article in Greek] law,
Note that there is no definite article “the” in the phrase “through the law.” Literally, it should read “through law.” Thus, Paul was dealing with more than the Mosaic Law here; he was dealing with the principle of God’s law in the broadest sense—any standard that He might have. Salvation is not through the “law of God.” There was no law in God’s arrangement for the salvation of Abraham’s soul; God saved him solely by faith.
Note also that God’s promise was to Abraham’s offspring as well as to Abraham himself. The promise of Genesis 15:6, that Abraham would be justified by faith, applies to anyone who accepts the principle of justification by faith.
God did not give the Mosaic Law until 500 years after Abraham. God did not give the Abrahamic covenant to Abraham “through the law” (Ge 12-15). The word “not” is emphatic in Greek; there is no question that God justified Abraham by faith and not by the law. The ratification of the “promise” preceded the “law” by 430 years (Ga 3:17).
but [strong contrast] through the righteousness of faith.
Once again, Paul argued that imputed righteousness comes by “faith.” There is no righteous quality in faith itself, but faith is essentially trust in God’s promises. God never accepts any righteousness other than the “righteousness of faith.”
The Greek word for “but” shows strong contrast. There is a strong contrast between being right before God by faith and by works of the law.
Paul would later develop the point that there were different kinds of Israelites. All people in Israel were not true Israelites. Abraham was a Gentile, but the thing that distinguished him as a true Israelite was regeneration (Ro 9:6-14). Abraham’s line did not go down through Ishmael, the unregenerate son, but through Isaac, the regenerate son. Isaac had two sons: Esau and Jacob; Jacob was regenerate, but Esau unregenerate. There were three different kinds of Jews: (1) racial, who were Jews by genes, (2) religious but not regenerate, who tried to be saved by keeping the law, and (3) the regenerate Jew, who believed the promise to Abraham. Jesus already fulfilled the salvation aspect of the Abrahamic promise (Ge 15:6).
Our salvation rests on God’s unconditional covenant with us.
Salvation by the law automatically cancels out faith. God unilaterally gave us salvation without any cause in us. Only God Himself could provide perfect salvation; nothing in us could measure up to God’s standards. It is necessary to abandon any claim to self-sufficiency for this salvation. Nothing in our actions can abrogate God’s covenant with us because the covenant does not depend upon us but upon God Himself. No failure on our part will change that.
The religious Jew, Nicodemus of Jesus’ day, needed to be regenerated (Jn 3). He was racially a Jew and a religious Pharisee, but he was not born again. Many people of our day are religious but lost.