Romans 4:13–16—God’s promise, human faith, and God’s grace.

So far in this “reckoning” chapter, Paul has built his argument on the great truth of Genesis 15:6. Abraham believed God, and God reckoned Abraham righteous on the basis of his faith. Now Paul points to another significant truth in the two verses that precede this divine act of reckoning.

God came to Abraham in a vision and told him that he would have his “very own son” who would be Abraham’s heir (15:4). Then God brought Abraham outside and told him to look up at the countless stars. “So shall your offspring be,” God told him (verse 5). We are not done with reckoning in this chapter, but now attention pivots from Abraham’s belief in the promise to the nature of the promise itself.

Colin Kruse ties together well the themes of both reckoning and promise: “Abraham believed the promise, his faith in the promise of God was credited to him as righteousness, and this was the ground upon which God would fulfill the promises he made to him.”

God’s promise comes from faith
A promise cannot come from the law, Paul says in verse 13, but through faith, which is the only route to righteousness. Richard Longenecker points out in his new Romans commentary that this verse is the thesis statement for the second half of Paul’s discussion of Abraham’s faith.

Here is how I understand verse 13: In regard to the law, Paul means (1) that God did not intend to use the law as a means of offering a promise and (2) that a person cannot obtain a promise by obedience to the law. In regard to faith, Paul means (1) that a person grabs ahold of the promise by believing the promise giver and (2) that faith is the route to righteousness.

These truths apply to both Abraham “and his offspring,” who include everyone who has believed God throughout salvation history. If you are a follower of Jesus Christ, having received and believed the gospel, you are one of Abraham’s offspring and you, like Abraham, are reckoned righteous through your faith.

The problem of the law
Verses 14 and 15 offer two reasons why the promise could not come through the law. First, if the promise could be obtained through adherence to the law, faith would be without foundation, and the promise would be void and worthless. Second, law brings God’s wrath on lawbreakers. That’s not good news for us, because no one, except for Jesus, could obey the law.

Law clarifies accountability and makes disobedience obvious. Douglas Moo quotes Calvin: “He who is not instructed by the written law, when he sins, is not guilty of so great a transgression as is he who knowingly breaks and transgresses the law of God.”

The good news of grace
As we see in verse 16, God has offered his promise as an expression of his grace—Paul’s first mention of that word in this chapter, though he has contrasted “wages” earned through works (meaning law keeping) with the “gift” offered through faith (verse 4). God extends his grace to all of Abraham’s offspring in that he guarantees his promise to those who trust him in faith. Note the contrast: whereas law voids the promise, faith guarantees it.

Paul refers to two categories of Abraham’s offspring. The first one— “the adherent to the law”— is awkward to interpret, but it seems to have a different meaning here than it does in verse 14 where there, in the plural, it clearly means Jews who trusted in the law as a means to righteousness. Here in verse 16 Paul seems to have in mind a typical Jew who respected the law and also had the kind of faith Abraham did.

In the second category is the typical Gentile believer Paul describes as “one who shares the faith of Abraham.” To highlight the unity of both believing (saved) Jews and Gentiles in the church, Paul portrays Abraham as “the father of us all.” Bob Utley turns a nice phrase: “God called Abraham to call all mankind!”