1) The Meaning of Resurrection in Early Christianity
2) Jesus died on a cross
3) His tomb was found empty
4) His disciples had experiences in which they believed they had seen Jesus alive.
5) The persecutor Paul and skeptic James converted to Christian faith on the basis of similar experiences.
6) The alleged improbability of miracles.
(skip to the bottom for summary of points)
I'd like to address the issue of dying and rising gods in various pagan beliefs: Many of the examples that are usually given turn out, on closer inspection not to be talking about a 'resurrection' at all. For example, Aesculapius was struck by lightning and ascended to heaven - hardly the same thing as dying and then being brought back to life as is the case with the Jesus story. The first clear parallel to the Jesus story of a resurrection does not come until more than a century after the time of Jesus. The argument that the Jesus story was influenced by these pagan myths is not taken seriously by scholarship today. In any case, the main reason why I don't think those dying-rising god stories are relevant (even if it were shown that some of them with real resurrection parallels predate Christianity): Those stories were told as myths about legendary figures in the distant past. The stories about divine emperors and such never contained resurrection in the sense of dying and rising, so they don't really apply here. Furthermore, the pagans who told these myths never believed that resurrection was something that humans would experience. The prevailing view among pagans (by which I mean the non-Jewish world) was that when you die, your soul goes to a gloomy (or perhaps restful) afterlife with no hope of returning to your body. There was of course some belief in reincarnation, but this was different from resurrection in that, with resurrection, there is continuity between the one who dies and the one who comes back to life. In reincarnation, you don't return to your former body; you begin as a new person altogether. Having (hopefully) cleared that up, we can get a better idea of what 'resurrection' language meant when the early Christians used it.
I've already argued that pagans universally denied resurrection. What I mean by this is that no one in the pagan world believed that, after people died, there was any hope of returning to life in a physical, bodily sense. In any case, many pagan philosophers would not find such a thing appealing, since the body was often treated like a prison-house for the soul. When they denied resurrection, they were not denying life-after-death, but a two-stage event better described as life after 'life after death'; resurrection involved the second of these two stages. In the world of second-Temple Judaism, there were those who denied any kind of afterlife, those who believed in a disembodied immortality for the soul, and those who believed in resurrection (this two-stage event in which a person was raised into a renewed physical, bodily existence). Note: 'resurrection' language was never used to denote the second of these positions. There simply was no such thing as a 'non-bodily' resurrection. Resurrection always referred literally to a concrete, bodily event. Once you understand that resurrection always referred to a two-stage event (since resurrection was something that would not happen until the end of history) you can see that it would be quite strange for it to mean anything other than a physical event. Furthermore, no one ever believed that one person would be raised from the dead individually before the end of history. It was unheard of.
When the early Christians proclaimed that Jesus had been raised from the dead (I will discuss evidence for this in #4 of the posts above), there is no question about how their hearers would have understood them. Nobody would have automatically assumed that they were merely referring to his 'exaltation' into heaven.
Having said that, what do we find when we look at our earliest written Christian source, Paul, who is usually targeted for having a non-physical view of resurrection? I will limit myself to those letters that are universally acknowledged as authentic letters of Paul. In certain passages, Paul shows that he models the future resurrection of all believers on the resurrection of Jesus himself (e.g., 1 Cor. 15.23, Christ as the "firstfruits" of what is to come). In many passages it is abundantly clear that Paul believes in resurrection as a two-stage event, that is, that the dead in Christ are still waiting for resurrection happen (e.g., 1 Thessalonians 4.13-16). In other words, the dead have been dead for a while now, but Paul does not think of them as having already experienced resurrection. This would be very odd if he did not think of resurrection as a bodily event. In fact, he makes the bodily aspect of resurrection very clear in certain other passages. In Romans 8:11 Paul says, "If the Spirit of him who raised Jesus from the dead dwells in you, he who raised Christ from the dead will give life to your mortal bodies also through his Spirit that dwells in you." (Note the word "also".)
In Acts 17 Paul quotes from a third century BC poet. It doesn't logically follow that just because something is quoted in the New Testament, it must have been invented by the NT writers. In the same way, most scholars believe that the NT writers make use of early Christian oral traditions, which go back closer to the time of Jesus' death. The book of Acts in particular contains several sermon summaries which are usually dated to within twenty years of Jesus' death. In two of these summaries (Acts 2 and 13), the speakers clearly state that David died and his corpse experienced corruption or decay, but that Jesus' corpse did not experience corruption. Here, physical resurrection is clearly in view.
What does all of this prove? NOT that Jesus must have truly been raised from the dead. What this does prove is that when Paul and the early Christians proclaimed that Jesus had been raised from the dead, they meant it in the bodily sense. Why is this important? Well it shows that the common view that Paul and the disciples (or whoever the early Christians were, and whoever wrote the NT) believed in 'resurrection' as a non-bodily event is simply not true. What about the point about resurrection being a two-stage view? Why is this significant? Because it creates tremendous problems for anyone who wants to argue that the early Christians, in speaking of Christ's resurrection, were merely speaking of his exaltation to heaven. If 'resurrection' was mere exaltation, it would happen immediately upon death. Certainly there were later Christian writers who believed this, but notice that they no longer upheld resurrection as a two-stage view. Luke (and John, incidentally) both differentiate Jesus' resurrection from his ascension.
Phew! Sorry to make this so long but it seems to be necessary. I'll post more the next time I get the chance. By the way if you want to see a REALLY in-depth study of resurrection belief in the first-century world I highly recommend NT Wright's The Resurrection of the Son of God.
SUMMARY OF POINTS
1) dying-rising god stories lack real parallels to Jesus story; those who told the stories did not believe in resurrection as a reality for human beings
2) the non-Jewish world universally denied resurrection; many Jews believed in resurrection as a two-stage event involving the body of the deceased
3) Paul believed in resurrection as a two-stage event involving the body of the deceased (and believed Jesus had been raised bodily)
4) Other early Christians clearly affirmed bodily resurrection (Acts 2, 13)
5) Early Christians (including Paul) were not using resurrection language to affirm Jesus' mere 'exaltation' to heaven