I'm convinced that Romans 1:17 is the banner that flies over Romans:
δικαιοσύνη γὰρ θεοῦ ἐν αὐτῷ ἀποκαλύπτεται ἐκ πίστεως εἰς πίστιν, καθὼς γέγραπται· Ὁ δὲ δίκαιος ἐκ πίστεως ζήσεται.In [the gospel] the righteousness of God is revealed from pistis [of Christ] for pistis [of the nations, 1:5, 16:26], as it is written "The righteous from pistis shall live."
Notice how Romans 3:26 starts to explain how this works:
ἐν τῇ ἀνοχῇ τοῦ θεοῦ, πρὸς τὴν ἔνδειξιν τῆς δικαιοσύνης αὐτοῦ ἐν τῷ νῦν καιρῷ, εἰς τὸ εἶναι αὐτὸν δίκαιον καὶ δικαιοῦντα τὸν ἐκ πίστεως ἸησοῦIt was to show his righteousness at the present time, so that he might be just and the justifier of the one who is from the pistis of Jesus.
Jesus demonstrates pistis in his life, death, and resurrection and God justifies the one who participates in/shares in (one whose life is patterned from/ἐκ the source that is) the pistis of Jesus. From pistis (of Jesus), for pistis (of the nations).
Romans 4:16 taps into this same dynamic, only with Abraham as the "source" rather than Christ:
Διὰ τοῦτο ἐκ πίστεως, ἵνα κατὰ χάριν, εἰς τὸ εἶναι βεβαίαν τὴν ἐπαγγελίαν παντὶ τῷ σπέρματι, οὐ τῷ ἐκ τοῦ νόμου μόνον ἀλλὰ καὶ τῷ ἐκ πίστεως Ἀβραάμ (ὅς ἐστιν πατὴρ πάντων ἡμῶν,That is why it depends on faith, in order that the promise may rest on grace and be guaranteed to all his offspring—not only to the adherent of the law but also to the one who is from the pistis of Abraham, who is the father of us all,
ESV translates the underlined phrase here as "shares the faith of Abraham" but if you look at the Greek text, it's the exact same construct as the ending in 3:26. Why don't we translate the former text as "shares the faith of Jesus"? If I had to guess, I would venture to say our reformation theology doesn't allow us to.
I think what's going on here is that Jesus and Abraham both embody the gospel pattern of Romans 1:17. The pistis of one becomes the source that others share/participate in unto blessing/salvation. In this sense, Abraham is for Paul a type of Christ in his life of pistis.
For Christ, this pistis is death-defying embodied fidelity out of which God brings resurrection life (and enthronement over the nations).
For Abraham, this pistis is the exact same: death-defying embodied fidelity out of which God brings resurrection life. This is precisely why Paul uses the language he does in 4:17-21:
as it is written, “I have made you the father of many nations”—in the presence of the God in whom he believed, who gives life to the dead and calls into existence the things that do not exist. In hope he believed against hope, that he should become the father of many nations, as he had been told, “So shall your offspring be.” He did not weaken in faith when he considered his own body, which was as good as dead (since he was about a hundred years old), or when he considered the barrenness [literally 'deadness'—same root as the word in the previous clause used to describe his body] of Sarah's womb. No unbelief made him waver concerning the promise of God, but he grew strong in his faith as he gave glory to God, fully convinced that God was able to do what he had promised. (Romans 4:17–21,ESV)
Notice how Paul goes out of his way to talk about the concept of death in this passage. What is the result of this death-defying embodied fidelity in the case of Abraham?
That is why his faith was “counted to him as righteousness.” (Romans 4:22, ESV)
But this doesn't mean what we think it means because of the reformers (i.e. imputation). In context, given the narrative shape of Paul's commentary on Abraham's life, he is using this verse to speak of the birth of Isaac. In other words, Isaac's birth represents the resurrection life that God brings in response to ("that is why") Abraham's death-defying embodied fidelity.
So now, what's the upshot of this all for the Roman church and for us all who give pistis to Jesus?
But the words “it was counted to him” were not written for his sake alone, but for ours also. It will be counted to us who believe in him who raised from the dead Jesus our Lord, who was delivered up for our trespasses and raised for our justification. (Romans 4:23–25, ESV)
First point here is that the resurrection-like birth of Isaac isn't just for the sake of Abraham; it's for the sake of all Christ followers to show that God always responds with resurrection life to death-defying embodied fidelity. Now notice the "it will be counted..." future language. What is Paul saying? I think Paul's saying that if we too share in this death-defying embodied fidelity to the God who raised Jesus from the dead over the long haul (just like Abraham's fidelity was one that grew over time, v.20b), God will also give us resurrection life in response to our death-defying embodied fidelity. Jesus was raised for our justification in the sense that His vindication from death becomes our vindication from death as we share in/participate in His death-defying fidelity. So the gospel shape of Abraham's life is here to re-enforce the gospel shape of Jesus' life:
From pistis unto resurrection for pistis unto resurrection.
Sounds like exactly what Jesus taught:
...whoever loses his life for my sake will find it. (Matthew 16:25, ESV)
In other words, whoever perseveres in death-defying embodied fidelity will receive resurrection life.