What did they claim to see?
After Jesus' resurrection, eleven disciples -- the original twelve minus Judas -- claimed to have seen him. (Acts 1:13) These eleven disciples' experiences of seeing and speaking with the risen Jesus took place in an atmosphere of fear for their own safety and grief, rather than some kind of expectation or emotional excitement. (John 20:19)
Some disciples, specifically Thomas, reportedly reacted with open skepticism to others' accounts. (John 20:25). In Matthew's account, some followers of Jesus doubted him even upon initially seeing him (Matt. 28:17). All accounts describe the disciples' initial reactions as anything but expecting visions or being receptive to the idea that Jesus was alive.
These reported experiences were not brief and confusing episodes, but were public, multisensory, and were extended across time. As Peter J. Williams writes: “The resurrected Jesus is recorded as appearing in Judaea and in Galilee, in town and countryside, indoors and outdoors, in the morning, in the evening, by prior appointment and without prior appointment, close and distant, on a hill and by a lake, to groups of men and groups of women, to individuals and in groups of up to five hundred, sitting, standing, walking, eating and always talking.” (Can We Trust the Gospels? p 134. See Matthew 28, Luke 24, John 20-21, 1 Corinthians 15:3-8) These appearances were reportedly extended across the period of forty days and also involved Jesus inviting people to touch him. (Luke 24:39, John 20:27, Acts 1:3)
The disciples' assertion of a bodily resurrection is further supported by Peter's comparison of David's decay to Christ's immortal body in his Pentecost sermon: “Brethren, I may confidently say to you regarding the patriarch David that he both died and was buried, and his tomb is with us to this day. And so, because he was a prophet,...he looked ahead and spoke of the resurrection of the Christ, that he was neither abandoned to Hades, nor did His flesh suffer decay. This Jesus God raised up again, to which we are all witnesses .” (Acts 2:29-32)
In addition, we need to consider Jesus' appearance to Paul. Paul was a zealous Pharisee bent on persecuting the church. As an explanation for his dramatic change of heart, Paul gave the well-known account of an auditory and visual experience on the Damascus road. He said that he saw a bright light, saw Jesus, and spoke with him. Paul said that Jesus asked him why he was persecuting him, then told him to go to Damascus and await further instructions. This vision also had some intersubjective aspects as Saul's companions heard a voice but did not see anyone. (Acts 9:3-21) From that point on, Paul preached that Jesus was the Messiah and was risen from the dead. His mission was endorsed by Peter, James, and John and they accepted him as an apostle. (Gal. 1:18,2:2-9)
The elementary creed found in 1 Corinthians 15:3-8 summarizes Paul's gospel: "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...and last of all, as it were to one untimely born, he appeared to me also." The majority of scholars, even many very liberal scholars, trace this creed to the Jerusalem church and date it to the early 30s.
There are many arguments that this creed didn’t originate with Paul. The most popular is that the use of "delivered" and "received" in 1 Corinthians 15:3 and the rhythmic structure and parallelisms in 1 Corinthians 15:3-7.
The most popular theory is that Paul received this tradition while in Damascus, possibly from Ananias or other Christians there, which would place it within one to three years of Jesus' death. However, I should note that there are several other later possibilities Paul may have received the creed as well. This passage nevertheless has evidential value because it provides confirmation that the resurrection claim started with the apostolic eyewitnesses themselves.
Atheist NT scholar Gerd Lüdemann writes: “…the elements in the tradition are to be dated to the first two years after the crucifixion of Jesus…not later than three years… the formation of the appearance traditions mentioned in I Cor.15.3-8 falls into the time between 30 and 33 CE.” [The Resurrection of Jesus, pp. 171-72.]
A quote from not a particularly conservative scholar
“I am sure that the disciples saw Jesus after his death...Typical encounters with the recently deceased do not issue in claims about an empty tomb, nor do they lead to the founding of a new religion. And they certainly do not typically eat and drink, and they are not seen by crowds of up to five hundred people.”
- Rudolph Bultmann, The New Testament and Mythology in Kerygma and Myth: A Theological Debate. p. 38.
Bultmann was a leading 20th-century New Testament scholar known for his program to “demythologize” the New Testament—i.e., to interpret, according to the concepts of existentialist philosophy, the essential message of the New Testament that was expressed in mythical terms.