Before we can truly understand their behavior, we must look at what their mindset was to help us understand what was really going on. For those who have studied the Bible you know that the Messiah was supposed to liberate Israel from the Roman oppressors. He was not supposed to be executed by them. This is what made it so difficult for the Disciples to understand Jesus’ predictions about his death. So when we examine the behavior of the Disciples, we see a group of men who abandoned and denied Jesus at the time of his arrest and execution who suddenly turned into men who boldly and publicly proclaimed his resurrection to the point they were executed for it. We must ask ourselves what was the origin of this belief? There are really only two options: influence from either Jewish or Pagan sources (you can’t argue for Christian influence because Christian influence hadn’t been invented yet).
To argue the origin was from Pagan influences is absurd. People will often quote ancient Greek mythology stories involving a resurrection (unfortunately these people don’t realize the first traceable mythological resurrection story is dated to 100 years AFTER Jesus’ time). To claim that the early Disciples thought their friend would come back to life based on Greek folk tales would be like you thinking your friend came back from the dead because you saw the movie E.T. Clearly Pagan mythology is not the appropriate way to understand the resurrection story.
The second option is from Jewish influences. We know that the concept of the resurrection wasn’t a new concept for a Jew as it was found in many places throughout the Old Testament (Isaiah 26:19, Daniel 12:2, Ezekiel 37). However the Jewish belief of the resurrection was ALWAYS after the end of the world and NEVER before that. This is the frame of mind the disciples brought with them in approaching the resurrection. This helps explain why it was so hard for them to understand Jesus’ predictions about rising from the dead; the resurrection only occurs at the end of the world. Given the 1st century Jewish beliefs about resurrection you cannot explain the Disciples and other early Christians belief in the resurrection of Christ outside of the actual event itself
But let’s put this aside for a moment. I want to focus on what I think is the most powerful argument that the Disciples saw Jesus Christ raised from the dead. The Disciples were willing to die for their belief. Now let me be clear about this, being willing to die for a cause does not verify the truth of their statements, it just verifies the sincerity of their statements. (For example, the terrorists that flew into the world trade center were sincere in their beliefs that this horrific act would secure their place in paradise, but that doesn’t mean that the act actually did secure their place). Every single one of the Disciples (minus John who was banished to an island) and numerous other witnesses of Christ’s resurrection were executed for their belief in the resurrection. Now many of these people weren’t killed immediately. Some had up to 30+ years before their death. It just doesn’t make sense why someone would go 30+ years knowingly believing a lie and then giving their lives for that lie. So how do we know the Disciples died specifically because of their belief in Jesus? Well, in addition to the Bible we have several non-Biblical sources that record these accounts: Clement (1 Clement 5:2-7), Ignatius (Letter to Smyrna 3:2-3), Polycarp (To the Philippians 9:2), Dionysus of Corinth (cited by Eusebius in Eccleastical History 2:25:8), Tertullian (Scorpiace 15), and Origen (Contra Celsum 2:56, 77) are just a few.
It is very important that we take into consideration the behavior of the disciples after Christ’s resurrection. We know they believed they had seen the risen Jesus, despite having every reason to the contrary, to the point they willingly gave their lives in defense of that belief. That is powerful evidence! Perhaps Jewish Rabbi Pinchas Lapide said it best:
“This scared, frightened band of the apostles, which was just about to throw away everything in order to flee in despair to Galilee; when these peasants, shepherds, and fishermen, who betrayed and denied their master and then failed him miserably, suddenly could be changed overnight into a confident mission society, convinced of salvation and able to work with much more success after Easter than before Easter, then no vision or hallucination is sufficient to explain such a revolutionary transformation”