Paul wrote to the believers in Rome before he had been there to see them (Romans 1:13-17 NET).

I do not want you to be unaware, brothers and sisters, that I often intended to come to you (and was prevented until now), so that I may have some fruit even among you, just as I already have among the rest of the Gentiles.  I am a debtor both to the Greeks and to the barbarians, both to the wise and to the foolish.  Thus I am eager also to preach the gospel to you who are in Rome.  For I am not ashamed of the gospel,¹ for it is God’s power (δύναμις) for salvation to everyone who believes (πιστεύοντι, a form of πιστεύω), to the Jew first and also to the Greek.  For the righteousness (δικαιοσύνη) of God is revealed (ἀποκαλύπτεται, a form of ἀποκαλύπτω) in the gospel from faith (πίστεως, a form of πίστις) to faith (πίστιν, another form of πίστις), just as it is written, “The righteous (δίκαιος) by faith (πίστεως, a form of πίστις) will live.”

Paul listed two reasons why he was not ashamed of the Gospel.

And again Paul quoted from the Septuagint.

The difference between the Septuagint and the Greek text used to translate the NET is the single word μοῦ.  In other words the Septuagint was even clearer in the sense that it read my faith (or faithfulness), as spoken by God: “The righteous by my faithfulness will live.”  The contemporary Hebrew translation of Habakkuk 2:4 in the NET reads: the person of integrity will live because of his faithfulness.  Not surprisingly that sounds like one who by his own effort keeps the law.

As I begin to contrast Romans and 1 Corinthians I’m not suggesting that Paul was ashamed of the Gospel in Corinth.  On the contrary he clearly stated one of the reasons he was not ashamed of the Gospel when he wrote to the Corinthians: the message about the cross is foolishness to those who are perishing, but to us who are being saved it is the power (δύναμις) of God.²  I must contrast these two letters to overcome my own bias that Romans is the Gospel in theory and 1 Corinthians is the Gospel in practice; or, even worse, that Romans is the sales pitch and 1 Corinthians is what happens if one is foolish enough to take the sales pitch seriously.

Even as I began to hear, even as I began to want to hear, Romans as crazy, hopeful things—alarming-could-they-possibly-be-true-I’ve-never-heard-anything-like-these-things-in-my-life things—after I finished reading Romans I turned to 1 Corinthians.  Whatever I thought I learned in Romans was largely undone there.  However hopeful I became reading Romans, 1 Corinthians sobered me up and encouraged me to maintain my faith in my efforts to keep the law, even after the law became my paraphrase of Paul’s definition of God’s love.  The discovery that Paul’s letter to the Romans was probably written after 1 Corinthians was a watershed moment for me.

So, while Paul stated one of the reasons he was not ashamed of the Gospel in 1 Corinthians, I want to examine it in its context (1 Corinthians 1:18-25 NET).

For the message (λόγος) about the cross is foolishness (μωρία) to those who are perishing, but to us who are being saved it is the power (δύναμις) of God.  For it is written, “I will destroy the wisdom (σοφίαν, a form of σοφία) of the wise (σοφῶν, a form of σοφός), and I will thwart the cleverness (σύνεσιν, a form of σύνεσις) of the intelligent (συνετῶν, a form of συνετός).”  Where is the wise (σοφός) man?  Where is the expert in the Mosaic law?  Where is the debater (συζητητὴς) of this age?  Has God not made the wisdom (σοφίαν, a form of σοφία) of the³ world foolish (ἐμώρανεν, a form of μωραίνω)?  For since in the wisdom (σοφίᾳ) of God the world by its wisdom (σοφίας, another form of σοφία) did not know God, God was pleased to save those who believe (πιστεύοντας, a form of πιστεύω) by the foolishness (μωρίας, a form of μωρία) of preaching (κηρύγματος, a form of κήρυγμα).  For Jews demand miraculous signs⁴ and Greeks ask for wisdom (σοφίαν, a form of σοφία), but we preach (κηρύσσομεν, a form of κηρύσσω) about a crucified Christ, a stumbling block (σκάνδαλον) to Jews and foolishness (μωρίαν, another form of μωρία) to Gentiles.⁵  But to those who are called, both Jews and Greeks, Christ is the power (δύναμιν, a form of δύναμις) of God and the wisdom (σοφίαν, a form of σοφία) of God.  For the foolishness (μωρὸν, a form of μωρός) of God is wiser (σοφώτερον, a form of σοφώτερος) than human wisdom, and the weakness of God is⁶ stronger than human strength.

There is a defensiveness here that seems entirely unnecessary, particularly calling the proclamation of the Gospel the foolishness of preaching.  The σύνεσιν (a form of σύνεσις), the συνετῶν (a form of συνετός), the σοφός and the συζητητὴς (a form of συζητητής) lead my thoughts back to Athens, and persuade me that his address before the Areopagus meant more to Paul than Luke’s flippant comment⁷ about the Athenians would suggest.  At a minimum 1 Corinthians was written two years after that event, yet the tension of that confrontation in Paul’s writing is as fresh as if it just happened.  None of this is to say that I think anything above is untrue, just that that truth is presented defensively.

Saul was no slouch intellectually.  Add the mind of Christ to that and Paul was formidable beyond reckoning as a συζητητὴς (debater).  There was never any reason for him to feel defensive around those with a philosophical bent to their minds, unless his own confidence was shaken somehow.  It leads me to suspect that though Paul continued faithfully, though he went through the motions, at this particular moment he didn’t have a fully satisfying handle on things.  Consider by way of comparison the confidence that emanates from the similar opening of Romans.

I am a debtor (ὀφειλέτης) both to the Greeks and to the barbarians, both to the wise (σοφοῖς, another form of σοφός) and to the foolish (ἀνοήτοις, a form of ἀνόητος).  Thus I am eager (πρόθυμον, a form of πρόθυμος) also to preach the gospel (εὐαγγελίσασθαι, a form of εὐαγγελίζω) to you who are in Rome.⁸  I don’t care if you are a Greek, a barbarian, wise or foolish, Paul wrote, I owe you the Gospel, the whole Gospel and nothing but the Gospel.  And I’m ready, willing and able to proclaim it to you.  All hint of prejudice is gone.  I can’t discern, for instance, whether Paul thought of the Romans as wise or foolish.  There is no hint of defensiveness except perhaps the perceived need to say (Romans 1:16, 17 NET):

For I am not ashamed of the gospel, for it is God’s power for salvation to everyone who believes, to the Jew first and also to the Greek.  For the righteousness of God is revealed in the gospel from faith to faith, just as it is written, “The righteous by faith will live.”

As a matter of completeness Paul’s Old Testament quotation follows.

Apparently, Paul substituted a stronger word αθετησω (I will thwart, I will set aside) for κρύψω (I will hide) in the Septuagint.  The NET translation of the Hebrew is, Wise men will have nothing to say, the sages will have no explanations.⁹  But a footnote alerts the reader that the Hebrew is: “the wisdom of their wise ones will perish, the discernment of their discerning ones will keep hidden.”

Addendum: November 2, 2019
Tables comparing Habakkuk 2:4 and Isaiah 29:14 in the Tanakh, KJV and NET, and tables comparing the Greek of Habakkuk 2:4 and Isaiah 29:14 in the Septuagint (BLB and Elpenor), and tables of Romans 1:16; 1 Corinthians 1:20; 1:22, 23 and 1:25 comparing the NET and KJV follow.