The fact that the Pauline epistles do not mention a historical Jesus raises remarkable doubts about whether a historical Jesus existed.
Remember the Gospels and Acts were composed AFTER Paul's letters.
Gerd Lüdemann says:
"Not once does Paul refer to Jesus as a teacher, to his words as teaching, or to [any] Christians as disciples."
and
"Moreover, when Paul himself summarizes the content of his missionary preaching in Corinth (1 Cor. 2.1-2; 15.3-5), there is no hint that a narration of Jesus’ earthly life or a report of his earthly teachings was an essential part of it....In the letter to the Romans, which cannot presuppose the apostle’s missionary preaching and in which he attempts to summarize its main points, we find not a single direct citation of Jesus’ teaching."
According to Richard Carrier, Paul's letters indicate that Cephas etc. only knew Jesus from DREAMS, based on the Old Testament scriptures.
1 Cor. 15.:
"For I delivered to you as of first importance what I also received, that Christ died for our sins according to the Scriptures, and that He was buried, and that He was raised on the third day according to the Scriptures, and that He appeared to Cephas, then to the twelve. After that He appeared to more than five hundred brethren at one time, most of whom remain until now, but some have fallen asleep; then He appeared to James, then to all the apostles; and last of all, as to one untimely born, He appeared to me also."
The Scriptures Paul is referring to here are:
Septuagint version of Zechariah 3 and 6 gives the exact Greek name of Jesus, describing him as confronting Satan, being crowned king in heaven, called "the man named 'Rising'" who is said to rise from his place below, building up God’s house, given supreme authority over God’s domain and ending all sins in a single day.
Daniel 9 describes a messiah dying before the end of the world.
Isaiah 52-53 describes the cleansing of the world's sins by the death of a servant.
Psalm 22-24 describes the death-resurrection cycle.
Paul seems to refer to Jesus's brother, James, which seems to suggest that Jesus was a real person.
However, see the point made here:
Paul also never says Jesus had biological brothers. Brothers by birth or blood appear nowhere in Paul’s letters. He only knows of cultic brothers of the Lord: all baptized Christians, he says, are the adopted sons of God just like Jesus, and therefore Jesus is “the firstborn of many brethren” (OHJ, p. 108). In other words, all baptized Christians are for Paul brothers of the Lord, and in fact the only reason Christians are brothers of each other, is that they are all brothers of Jesus. Paul is never aware he needs to distinguish anyone as a brother of Jesus in any different kind of way. And indeed the only two times he uses the full phrase “brother of the Lord” (instead of its periphrasis “brother”), he needs to draw a distinction between apostolic and non-apostolic Christians (more on that below; but see OHJ, pp. 582-92).
See also this point from here:
Rather than simply say “I met two Apostles, Cephas and James the Brother of the Lord,” a way of saying it that would definitely mean Cephas was not whatever a “Brother of the Lord” was, Paul chose instead to say:
I did not go to Jerusalem to those who were Apostles before me [then]…[but] after three years I went to Jerusalem to visit Cephas and stayed with him for fifteen days. But I saw no other Apostles—just the Brother of the Lord James.
Carrier makes the following point in the peer-reviewed 2014 volume OHJ (pp. 588-590):
Whether Paul is actually lying about any of this is not relevant to what Paul wants the Galatians to think and thus what Paul means to say here. And what he means to say is that no one in Judea ever met him. He swears to this most emphatically (Gal. 1.20). He admits there were only two exceptions, Peter and James, and only for a brief time (and that years after he saw the Lord personally). But in saying so, why didn’t Paul just say ‘of them that were apostles before me [1.17] I met none except Peter and James [1.18-19]’? Why does he construct the convoluted sentence ‘I consulted with Peter, but another of the apostles I did not see, except James’? As L. Paul Trudinger puts it, ‘this would certainly be an odd way for Paul to say that he saw only two apostles, Peter and James’.[n. 98] To say that, a far simpler sentence would do. So why the complex sentence instead? Paul could perhaps mean that he consulted with Peter (historeô) but only saw James (eidô)—that is, he didn’t discuss anything with James. But if that were his point, he would make sure to emphasize it, since that would be essential to his argument. Yet he doesn’t. In fact, if he is saying that he saw none of the other apostles, that would entail he was claiming he did not consult with any, either.
So it’s just as likely, if not more so, that Paul means he met only the apostle Peter and only one other Judean Christian, a certain ‘brother James’. By calling him a brother of the Lord instead of an apostle, Paul is thus distinguishing this James from any apostles of the same name—just as we saw he used ‘brothers of the Lord’ to distinguish regular Christians from apostles in 1 Cor. 9.5. Indeed, this would explain his rare use of the complete phrase in only those two places: he otherwise uses the truncated ‘brother’ of his fellow Christians; yet every time he specifically distinguishes apostles from non-apostolic Christians he uses the full title for a member of the Christian congregation, ‘brother of the Lord’. This would be especially necessary to distinguish in such contexts ‘brothers of the apostles’ (which would include kin who were not believers) from ‘brothers of the Lord’, which also explains why he doesn’t truncate the phrase in precisely those two places.
The point is as follows (from here):
I here cite Trudinger’s peer reviewed article demonstrating that the grammatical construction Paul uses in Gal. 1:19 is comparative. In other words, “Other than the apostles I saw no one, except James the Lord’s brother.” Thus, the construction Paul is using says James is not an Apostle. And both Trudinger and Hans Dieter Betz (who wrote the Fortress Press commentary on Galatians) cite a number of peer reviewed experts who concur (OHJ, p. 590, n. 100). There were of course Jameses who were Apostles. So Paul chose this construction to make clear he didn’t mean one of them (or a biological brother of Cephas, for that matter). He meant a regular “Brother of the Lord,” an ordinary non-apostolic Christian. But a Christian all the same—which was important for Paul to mention, since he had to list every Christian he met on that visit, lest he be accused of concealing his contacts with anyone who knew the gospel at that time.
It's also remarkable that PhD scholars have misrepresented the letters of Paul in a way that you can easily check for yourself. Mark Goodacre totally misrepresented a passage from Paul in a way that you can check for yourself: https://www.youtube.com/watch?v=58dG-wWBPBI&t=1200. Ehrman also does this in a way that you can easily check: https://www.richardcarrier.info/archives/11516. This is not to say that they were consciously lying or that there's a big conspiracy or anything, but it should give you pause and make you think about what kind of expertise the scholarly consensus really rests on if people with PhDs in the field are making demonstrably false claims about what it says in the Pauline epistles.