Thank you, John Loftus, for the invitation and opportunity to express some of my ideas.
Dr. Steve Mason has said on a couple of MythVision Podcasts that some of the epistles have passages that seem to be responding to something that has been asked or stated here and uses a telephone analogy to describe it here. He makes a point that this lends authenticity to the epistle, but we can only guess what has prompted the response. This article attempts to show that Paul and James were interacting in that way.
Paul quotes from the Septuagint version of Leviticus 19:18 and follows Rabbi Hillel's commentary, "That which is hateful to you, do not do unto your fellow. That is the whole Torah; the rest is the explanation; go and learn." :
Galatians 5:14 (NRSV)14 For the whole law is summed up in a single commandment, “You shall love your neighbor as yourself [αγαπησεις τον πλησιον σου ως σεαυτον (verbatim from Leviticus 19:18 LXX)].”
James quotes the same Leviticus passage and says it is a good start but denies what Paul has said about it summing up the whole law:
James 2:8-11 (NRSV)8 You do well if you really fulfill the royal law according to the scripture, “You shall love your neighbor as yourself [αγαπησεις τον πλησιον σου ως σεαυτον].” 9 But if you show partiality, you commit sin and are convicted by the law as transgressors. 10 For whoever keeps the whole law but fails in one point has become accountable for all of it. 11 For the one who said, “You shall not commit adultery [μη μοιχευσης],” also said, “You shall not murder [μη φονευσης].” Now if you do not commit adultery but if you murder, you have become a transgressor of the law.
Paul has a response to James' argument in Romans 13. Paul quotes the same two commandments James quoted, in the same wrong order, then adds two more and cites the Leviticus passage again. He sums it up by pointing out that one will do what is in the law just out of love for the neighbor, paying more homage to Hillel.
Romans 13:8-10 (NRSV)8 Owe no one anything, except to love one another; for the one who loves another has fulfilled the law. 9 The commandments, “You shall not commit adultery [ου μοιχευσεις (verbatim from Exodus 20:14 LXX and Deuteronomy 5:18 LXX)]; You shall not murder [ου φονευσεις (verbatim from Exodus 20:13 LXX and Deuteronomy 5:17 LXX)]; You shall not steal [ου κλεψεις (verbatim from Exodus 20:15 LXX and Deuteronomy 5:19 LXX)]; You shall not covet [ουκ επιθυμησεις (verbatim from Exodus 20:17 LXX and Deuteronomy 5:21 LXX)]”; and any other commandment, are summed up in this word, “Love your neighbor as yourself [αγαπησεις τον πλησιον σου ως σεαυτον].” 10 Love does no wrong to a neighbor; therefore, love is the fulfilling of the law.
In Galatians 3, Paul argues that faith is what is important. He quotes Genesis 15:6 about Abraham being reckoned as righteous when he believed.
Galatians 3:6-9 (NRSV)6 Just as Abraham “believed God, and it was reckoned to him as righteousness,” [τω θεω και ελογισθη αυτω εις δικαιοσυνην] 7 so, you see, those who believe are the descendants of Abraham. 8 And the scripture, foreseeing that God would justify the Gentiles by faith, declared the gospel beforehand to Abraham, saying, “All the Gentiles shall be blessed in you.” 9 For this reason, those who believe are blessed with Abraham who believed.
James argues that Abraham was justified by works rather than faith.
James 2:21-23 (NRSV)21 Was not our ancestor Abraham justified by works when he offered his son Isaac on the altar? 22 You see that faith was active along with his works, and faith was brought to completion by the works. 23 Thus the scripture was fulfilled that says, “Abraham believed God, and it was reckoned to him as righteousness,” [τω θεω και ελογισθη αυτω εις δικαιοσυνην] and he was called the friend of God.
In Romans, Paul asserts that Abraham was not justified by works because he would then have something to brag about. Again he quotes Genesis 15:6.
Romans 4:1-3 (NRSV)1 What then are we to say was gained by Abraham, our ancestor according to the flesh? 2 For if Abraham was justified by works, he has something to boast about, but not before God. 3 For what does the scripture say? “Abraham believed God, and it was reckoned to him as righteousness.” [τω θεω και ελογισθη αυτω εις δικαιοσυνην]
Further down, Paul points out that Abraham was justified by faith (in Genesis 15) before he was even circumcised (in Genesis 17) and before he did those works.
Romans 4:10-12 (NRSV)10 How then was it reckoned to him? Was it before or after he had been circumcised? It was not after, but before he was circumcised. 11 He received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised. The purpose was to make him the ancestor of all who believe without being circumcised and who thus have righteousness reckoned to them, 12 and likewise the ancestor of the circumcised who are not only circumcised but who also follow the example of the faith that our ancestor Abraham had before he was circumcised.
Paul had argued that people are justified by faith and not by works in:
Galatians 2:16 (NRSV)16 yet we know that a person is justified [δικαιουται ανθρωπος] not by the works of the law but through faith [εκ πιστεως] in Jesus Christ. And we have come to believe in Christ Jesus, so that we might be justified by faith in Christ, and not [και ουκ] by doing the works of the law, because no one will be justified by the works [οτι εξ εργων] of the law. [(εξ εργων) νομου ου δικαιωθησεται πασα σαρξ]
Galatians 3:11 (NRSV)11 Now it is evident that no one is justified [δικαιουται] before God by the law; for “The one who is righteous will live by faith.” [οτι ο δικαιος εκ πιστεως ζησεται]
James continues his argument by directly contradicting Paul in those verses.
James 2:24 (NRSV)24 You see [ορατε] that a person is justified [δικαιουται ανθρωπος] by works [οτι εξ εργων] and not [και ουκ] by faith [εκ πιστεως] alone [μονον].
Note that except for the first and last Greek words in James 2:24, it is composed of two and three word phrases that had been used Galatians 2:16. The phrase "και ουκ" for "and not" is used all over the place. The phrase "εκ πιστεως" for "by faith" is found 12 times in Romans and 9 times in Galatians but it is used but once in James 2:24, once in Hebrews 10:38, and once in Habakkuk 2:4. Both of the phrases "δικαιουται ανθρωπος" for "a person is justified" and "οτι εξ εργων" for "by the works" are found only in these two verses.
Paul stuck by his guns and responded in Romans:
Romans 3:20 (NRSV)20 For “no human being will be justified in his sight” by deeds prescribed by the law, [εξ εργων νομου ου δικαιωθησεται πασα σαρξ] for through the law comes the knowledge of sin.Romans 3:28 (NRSV)28 For we hold that a person is justified by faith apart from works prescribed by the law.
There are also many verses where Paul and James agree in the Galatians > James > Romans sequence.
2 Corinthians is thought by some to be a compilation of multiple letters from Paul. The latter chapters use a lot of words about "boasting" and "arrogance." About a third of words in the MGNT that begin with root "καυχ-" are found in chapters 10, 11, and 12 of 2 Corinthians.
There are passages where Paul tells of his travel plans that failed to come to fruition:
2 Corinthians 1:15-16 (NRSV)15 Since I was sure of this, I wanted to come to you first, so that you might have a double favor; 16 I wanted to visit you on my way to Macedonia, and to come back to you from Macedonia and have you send me on to Judea.1 Thessalonians 2:17-19 (NRSV)17 As for us, brothers and sisters, when for a short time we were made orphans by being separated from you—in person, not in heart—we longed with great eagerness to see you face to face. 18 For we wanted to come to you—certainly I, Paul, wanted to again and again—but Satan blocked our way. 19 For what is our hope or joy or crown of boasting (καυχησεως) before our Lord Jesus at his coming? Is it not you?
James may be commenting on either passage and gives some advice and comments about boasting and arrogance:
James 4:13-16 (NRSV)13 Come now, you who say, “Today or tomorrow we will go to such and such a town and spend a year there, doing business and making money.” 14 Yet you do not even know what tomorrow will bring. What is your life? For you are a mist that appears for a little while and then vanishes. 15 Instead you ought to say, “If the Lord wishes (υμας εαν ο κυριος θεληση και), we will live and do this or that.” 16 As it is, you boast (καυχασθε) in your arrogance (αλαζονειαις); all such boasting (καυχησις) is evil.
Paul may have assumed James meant the 2 Corinthians passage since he responded in a letter to the Corinthians by repeating the advice verbatim and says he will look for those arrogant people.
1 Corinthians 4:19 (NRSV)19 But I will come to you soon, if the Lord wills, and (υμας εαν ο κυριος θεληση και) I will find out not the talk of these arrogant (πεφυσιωμενων: literally "puffed up") people but their power.
The Epistle of James was addressed to "To the twelve tribes which are scattered abroad" so Paul likely would have multiple chances to have seen it. James appears to respond to what Paul had written, especially in the Epistle to the Galatians. Paul appears to respond to the Epistle of James in the Epistle to the Romans and in 1 Corinthians. That means Paul recognized that the Epistle of James was responding to him and that he thought it was written by the James he met in Jerusalem.
 Wikipedia, "Hillel the Elder", https://en.wikipedia.org/wiki/Hillel_the_Elder, retrieved 4/21/2023.