I have doubts about the truthfulness of Christianity. This is difficult for me, because my Christian faith was very precious to me for basically my entire life. But, there has been a shift from "accept Christianity, in spite of difficulties" to "do not believe, because of difficulties", for me personally.
Firstly, Jesus saying that He would return within the lifespan of the audiences listening to him, once I examined all the verses together (Matthew 10:23, 16:27-28, 24:3-34), and took a consistent meaning of "this generation" in Matthew, where it means "this generation" of people currently living (Matthew 11:16, 12:41-42, 12:45, 17:17, 23:36), was a major break for me. Accepting that God, without explicitly saying so, "delayed Jesus's second coming", in spite of what Jesus said (and especially how he said it), is really difficult. The way that the writers of the New Testament speak of Jesus's return also indicates that they thought it would be very soon (Romans 13:11-12, 16:20: 1 Corinthians 7:29, 10:11: Philippians 4:5: 1 Thessalonians 4:15-17, Hebrews 9:26, 10:37, James 5:7-8: 1 Peter 4:7 Revelation 1:1, 1:3, 22:6). The only book that appears to deal with it not taking place is 2 Peter, which has an incredible amount of controversy surrounding it (rejected early, apparently quotes Jude, very different from 1 Peter).
Additionally, I have a sort of meta-problem regarding what allegedly took place in the resurrection. The resurrection of Jesus was supposed to be the ultimate vindication of him by the God of the universe; a divine endorsement of him, and his message. Unfortunately, his resurrection was not made a public spectacle, to where there would be no doubt that it took place. He did not go into the Temple in Jerusalem, and proclaim to Caiaphas, "It is me, I have returned from the dead". He did not appear before all Jerusalem, so that the city would be in uproar, and there could be no doubt that the one who they had seen publicly killed in a grievous way was now standing before them whole. Instead, unfortunately, his alleged resurrection was only witnessed by a few close associates, and in private, whereafter, he vanished and was never seen again. And, none of the writings of these close associates who saw him, if they ever made any, survive, with the exception of maybe one letter alleged to be from Peter, and "John's" alleged writings, which almost no one who specializes in the topic believes are actually written by John the Apostle. The meta question would be, if God had raised Jesus from the dead, why not vindicate him publicly in such a way that none could deny it? Why instead make the object of faith for all who came in the future be the disputed writings alleged to come from a few close followers? Why not have Jesus stay and teach for a few years or decades, so that all doubts would be banished forever?
Additionally, the New Testament's descriptions of miracles are not really possible to reconcile with the historical growth of early Christianity. According to the New Testament, Jesus prolifically performed many undeniable miracles, some of which were in front of thousands of witnesses. The New Testament also records the resurrection of dead saints, who then made public appearances in Jerusalem (Matthew 27:52-53). It of course records the resurrection of Jesus, which was seen by at least 500 people (1 Corinthians 15:3-8). It then records a lengthy miraculous ministry of the Apostles, in which they performed miracles in front of thousands of people (Acts 2:41). Yet, for all this, according to the historical record, Christianity was a relatively small movement, having about 10,000 followers by the end of the first century (the exact number is not important - anything less than an empire-wide explosion does not make sense, in light of what the Bible claims). This is why there is such a scant written record from the first and second centuries. It remained a small, relatively unimportant religious movement, and most Jews ignored it.
This cannot simply be dismissed. If one sees an undeniable miracle, they do not simply move on with their lives as if nothing happened. Instead, it would become a pivotal highlight of their life. They would not only immediately tell their friends and family, but it would become a story that they would tell over, and over, and over again, deep into their old age, to anyone who would listen. Far lesser stories are told by grandparents today to the point where their audience, if familiar with them, can practically recite them verbatim. How much more common would this be in an oral culture, where recounting stories would constitute a primary form of entertainment for most people?
Consider, for instance, Matthew's resurrection event, in which dead saints were said to appear to many in Jerusalem after the resurrection of Jesus (Matthew 27:52-53). Consider if someone who was dead came to your own house. Quickly, you would tell your neighbors. Your mother would go down to the marketplace, and tell all of her friends. Within a few hours, everyone in your town would know. Within a day, people from different cities would know, and some would come to see. It would be the most important event that ever happened to you. The entire town would be in an uproar for the entirety of the event, and it would be famous in short order. For decades, everyone in that town would remember it as the event of a lifetime, and the story would persist for generations. This is how actual people would react to a miracle. The New Testament, however, has so many incredible, world-shaking miracles take place, and yet historical reality shows that there was no great conversion of Israel, let alone the Roman Empire, in the century in which all of these extraordinary events were supposed to be taking place. The 500 alleged witnesses of the resurrection apparently could not be bothered to tell anyone they knew, or have even a single person write down and preserve what they had seen in a way that would be traceable to them. If these witnesses ever existed at all, it appears that they simply disappeared into history, as nothing exits to indicate who they were, or that they ever saw anything.
However, if thousands had seen these undeniable miracles, as the New Testament describes, then one would expect such a massive preponderance of evidence for them that it could not be denied that something took place, even from a secular point of view. There would be government accounts of uproar, and commotion, and mass conversion, and many firsthand reports of the events themselves, from different perspectives. This is not what is seen at all. Christianity remained extremely small, and Jerusalem and Israel continued on as if nothing particularly remarkable happened, with many converts coming from Gentile areas far from the founding location, and away from any eyewitnesses. This is contrary to all human nature, and how people who would have seen a miracle would actually behave, and what their impact on their communities would have been. Therefore, it is very likely that the events never happened.
Additionally, the nature of Scripture is a big problem for me. Why should anyone believe, for instance, that the epistle of Jude was inspired by the God of the universe? Or that God sanctioned what was written in the book of Hebrews, or James? Or that those who took it upon themselves to write Gospels actually had all the facts concerning Jesus, and represented him accurately? And where they disagree, which of them was more accurate to what Jesus originally said, or did, or what happened? Who are these men? Are they reliable? Are the honest? Are they intelligent? They did not claim a divine commission for writing. So, why should I believe that their writings are protected from error in any sense? Their works being very well-written, or quoting Old Testament scripture, or agreeing with other works in the corpus, or being attached to those who allegedly knew Jesus in some way, does not mean that the God of the universe protected them from error in some way while they wrote.
Consider also the position that since Jesus was the Christ, commissioned with a message from God, we must listen to everything that he taught. I cannot actually do that. I cannot speak to Jesus. There is nothing written by him. And, there is no way to read what he said, without first putting one's faith in human beings, and supposing that their representation of him is accurate. This is putting faith in men, not Jesus, and not God, because the best I can do is believe the witness of men other than Jesus, that he actually said what they present as being said by him. Additionally, I have to rely on the witness of men who copied these writings, and translated them. This is squarely putting one's faith in men. God never promised to me that He would inspire these writings, or preserve them, nor did He tell me to read them, and trust them as legitimate. Rather, men have told me that they are legitimate communication from God, and I am to trust them at every step in the alleged transmission process, from God to me, in a roundabout way. And, given how loose "John" appeared to have been with the words of Jesus, and given that several Gospel authors either trimmed, or embellished his words in places (given the differences in parallel passages in the various accounts), I have cause to doubt that these authors were merely acting as sounding boards, rather than editors and redactors. And, I cannot see their sources, or interview those who they may have interviewed, or speak to them, either. The same point made in this paragraph could be applied to Old Testament books in which God is allegedly being quoted.
This issue of the object of one's faith is a major sticking point for me. In Christianity, the object of my faith would not actually be Jesus, as I have never met Jesus, nor heard him speak. He has not told me anything. It would not be God, as I have never met God, and never heard Him speak. Neither God, nor Jesus ever told me to trust the Bible. So, my faith would not be in them. It would be in the men who are purporting to speak for them, and also those who gave me the writings which allegedly came from those men. The same is true of the Old Testament prophets. My faith in reading Isaiah is not in God. It is not even in Isaiah. It is in the writers, transmitters, editors, and translators of the book of Isaiah, that it actually represents what the man Isaiah said or taught. If I first put my faith in these men, then I can put my faith in the man Isaiah. But, I have never met Isaiah. I never witnessed whatever miracles that he may have performed as evidence of a divine commission. So, I have no valid reason to place my faith in the man Isaiah, that he is speaking for God. But, if I were to, my faith would still not be in God, but in Isaiah. Short of actually seeing the miraculous verification of his work, the best one can do is put their faith in man. And, since no Christians living today have ever seen any of the undeniably supernatural miracles of the Bible take place, none of them can actually say that they have their faith in God, properly speaking. They have their faith in men, who professed at various times to speak for God, and those who claimed to transmit their words. This means that denying the authority of the Bible is not denying God, or professing lack of faith in God. God never told me to read it, or trust it. If He did so, I would certainly do it. Refusing to do it after He told me so could be called a lack of faith in God. But refusing to trust the authenticity of the current Bible is something altogether different.
But, this leap of faith is a bit of a brick wall. No matter how much one tries, they will never be able to go back in time, and actually verify with certainty that what they are reading actually happened. This is very frustrating for those who are aiming to stake their lives on the Bible. There is a point in which no more certainty can be achieved, and one ultimately has to trust in the authors, transmitters, and editors of the books that they are reading within the Bible, even in spite of massive problems. An "apologist answer" here may be that "God requires faith". But, as already discussed, this would be faith in human beings. If God Himself told me something, I would believe it, even if it was contrary to my own intuition, or seemed unlikely to me. That would be faith in God. This is something different. Additionally, God, in this scheme, would actually not have required faith for the extraordinarily lucky few who got to see the alleged supernatural confirmation of these writings. They would have been able to say that they had faith in God. However, for all others, their faith would, at best, be in mankind. This same brick wall comes into play when there are doctrinal controversies, and one cannot simply ask the authors of these books what they meant, or specifically believed, but I digress.
Therefore, before even getting into more specific examples of difficulties with the Bible itself (unlikely stories, possible contradictions, possible historical problems, etc.), given some of the above considerations, I cannot say that I believe in the truthfulness of Christianity. When I read the Bible, I have serious doubts as to whether I am reading a message from God, or the heavily altered, edited, and redacted words of various people, who were writing what came to their minds. And, I cannot interact with any of the authors, neither do I have any supernatural proof for their claims to speak for God, nor has God told me to place my trust in it. This makes the religion of Christianity unbelievable, in my opinion.
In this section, I will list some specific examples of other issues from the Bible which caused me to tip toward unbelief. Note that I will cite the SBL Study Bible to substantiate some points below, but the same points could be made by appealing to many other contemporary scholarly publications:
There are many other issues, in addition to the ones explained above, but the above are demonstrative of why I do not personally believe that the Bible is inspired by God anymore.