Famous examples that are candidates for interpolation include Romans 1:3 (and surrounding), Galatians 1:19 (and surrounding), and the phrase in Galatians 4:4.
Just because these three passages cause problems for mythicists, that does not mean they are famous examples.
About Romans 1:3 & surroundings:
Here I explained why Paul would have written (or inserted a hymn) Ro 1:3-6 (therefore against the possibility of interpolation):
>> But why did Paul suddenly announce the Son (Jesus) "come of David's seed according to flesh"
, when he never made use of it next (except much later and briefly in Romans 15:12)? And when Paul never depicted Jesus as King? And right at the very beginning of his epistle?
Paul was addressing a remote audience whom he never met (except a few, according to Romans 16:3-16a, likely in cities such as Corinth & Ephesus, before they moved to Rome), but expected his letter to be read also by/to Jews (Romans 2:17, etc.). Such a statement would immediately attract their attention (favorably). But what about the others, the Gentiles? Could Paul have taken the risk to turn them off early on by claiming a (very much) Jewish
attribute (unheard of before, according to Earl), and not even necessary for his ensuing discussion? Of course not!
Therefore, Jesus, as "Son of David", had to be already widely admitted, and Paul knew it. So he could mention it, out of the blue, without upsetting (or confusing!) anyone.
Note: in the front of his epistle (up to 2:17), it seems Paul tried to soften up his Jewish audience:
a) "concerning his Son (come of David's seed according to flesh,)"
(Romans 1:3 Darby)
b) "marked out Son of God in power, ... by resurrection of
(Romans 1:4 Darby)
It appears here there is no pre-existence for the Son, who is revealed only by his (alleged) resurrection.
c) Jesus is never identified as solely "(the) Lord".
d) From 1:10 to 2:15, there are twenty-four mentions of "God" in a row, with no Jesus/Son/Lord/Christ in between.
It is only after alluding to God's wrath to come and writing "in [the] day when God shall judge the secrets of men, according to my glad tidings, by Jesus Christ."
(2:16 Darby) that Paul confronted the Jews about the Law and circumcision. <<
And Ro 1:3, as written by Paul, is confirmed by Ro 15:12: “And again, Esaias saith, There shall be a root of Jesse, and he that shall rise to reign over the Gentiles; in him shall the Gentiles trust. ”
About the phrase in Galatians 4:4: http://historical-jesus.info/18.html
After analyzing Gal 3:7-4:7, I concluded: Paul used the common knowledge Jesus had been an earthly man (from a woman) and a Jew (as descendant of Abraham) in order to clinch a long & complicated argument. If the existence of Jesus on earth was not accepted or even doubted, then the argument would simply not work.
Here is my analysis:
>> Paul started by making a claim: "But to Abraham were the promises addressed, and to his seed: he does not say, And to seeds, as of many; but as of one, And to thy seed; which is Christ."
(3:16 Darby). That seems to refer to Genesis 17-22 but it is never specified here according to Paul's words.
Anyway, the promise is about inheritance (3:18) for all (Gentiles and Jews --3:8, 14, 28-29) but that is put on hold by the Law "until the seed
['erchomai', clear expression of a coming to occur] to whom the promise was made"
(3:16, 19). Then everyone would be liberated from the Law by Christ (3:13, 22-25) & his crucifixion (3:13) and "the promise, on the principle of faith of Jesus Christ, should be given to those that believe."
(3:22), allowing Paul's Galatians to be God's sons & heirs and (by "adoption"?) seed of Abraham (3:7, 29).
What remains is for the Son/Christ to come as the seed of Abraham, that is as a Jew and earthly human (as other seeds of Abraham, like Paul
(Ro 11:1), Jews of Israelite descent
(Ro 9:7), other apostles
(2 Cor 11:20)), in order to enable the promise. So we have:
Gal 4:4-7 Darby "but when the fullness of the time was come, God sent forth his Son, come of woman
[as an earthly human],come under law
[as a Jew would be], that he might redeem those under law, that we might receive sonship. But because you are
[Greek present tense] sons ... So you are
[present again] no longer bondman, but son ..."
So Paul was thinking about an earthly "flesh & blood" mother! And Christ had already come and gone (1:1)!
About Galatians 1:19 (and surrounding):
What is the best explanation for "James, the brother of the Lord"
This is the first reference of “James”
in ‘Galatians’. But at the time (around 38) of Paul’s first visit to Jerusalem after his conversion (as narrated in Galatians 1:18-20) there was another prominent member of the “church of Jerusalem” named James, the brother of John, who got executed around 42 (according to Acts 12:1-2). Therefore, Paul probably wanted to identify the “James”
he met then, more so due to this one becoming most important later.
Because that other James was not a brother of Jesus, referring to James in Galatians 1:19 as "the brother of the Lord"
would remove any confusion.
Also we have the testimony of Josephus in Antiquities (“the brother of Jesus so-called Christ, James by name”
): another interpolation to demonstrate?