Abraham’s faith was demonstrated before the law was given by many hundreds of years, thus he was not saved by the law. Chronologically this seems obvious, but the Second Temple period texts cited above indicate at least some Jews looked to Abraham as a proto-Jew or “first proselyte.” Kruse cites Mekhilta Ex. 22:20 (101a), “Abraham called himself a proselyte (ger), for it is written, I am a stranger (ger) and a sojourner with you (Gen. 23:4) (Romans, 210).
Paul says Abraham was promised his offspring would become “heirs of the world,” although Genesis defines the land promise narrowly. But by the first century, there were several Second Temple texts that expanded that land promise to include the whole world (Sirach 44:21; Jub. 32:19; 1 Enoch 5:7, 4 Ezra 6:55-59). Jesus says “the meek will inherit the earth” (Matt 5:5), very similar to 1 Enoch 5:7.
Sirach 44:21 (NRSV) Therefore the Lord assured him with an oath that the nations would be blessed through his offspring; that he would make him as numerous as the dust of the earth, and exalt his offspring like the stars, and give them an inheritance from sea to sea and from the Euphrates to the ends of the earth.
1 Enoch 5:7 But to the elect there shall be light, joy, and peace, and they shall inherit the earth. To you, wicked ones, on the contrary, there will be a curse.
Jubilees 32:19 And I shall give to your seed all of the land under heaven and they will rule in all nations as they have desired. And after this all of the earth will be gathered together and they will inherit it forever.”
All of these texts are based on the Hebrew Bible Isaiah 2, for example, describes Zion as the exalted mountain to which all the nations will stream. From Zion the Lord himself will reign and the nations will come to Zion to “learn the ways of the Lord.” In Daniel 7:14 the Ancient of Days gives a “son of man” authority to rule over all of the nations in an “everlasting dominion that will never end.” Even a text like Psalm 2 indicates the Lord’s anointed king could potentially receive the nations as an inheritance.
Paul certainly looks forward to a future kingdom (1 Cor 15:20-28, Phil 2:5-11), but in this text the descendants of Abraham are those who are being justified by faith in Jesus. Paul has a Jewish, apocalyptic view of what God will do in the future. But here in Romans 4 he connects the “offspring of Abraham” with those who have faith in Jesus, the “in Christ” people. The nations are the Gentiles who are being justified by faith and not works of the Law.
Imagine how this would sound to Roman Christians who were used to hearing that Rome controlled the world (Jewett, Romans, 325). It is unimaginable that an extremely small group of followers of Jesus would somehow challenge the Roman Empire. From the perspective of the mid-first century, Christianity had no impact on the culture of the Empire. But it was not long at all before Christianity began to challenge the thinking of the Roman world.