Why did the early church apply the word resurrection to Jesus? If they wanted to say that Jesus was alive and had triumphed over his enemies and was exalted by God, then why not say that? Why not say that he had been bodily assumed into Heaven and was now with the Father? The early proclamation that Jesus rose from the dead is a puzzle for naturalists, because it seems unexpected given what most Jews believed about the concept of resurrection. Jews didn’t have any concept of an individual resurrection before the day of judgment. Resurrection was something that happened to all the righteous at the end of the world. Not to one person.

Here’s a post from Tough Questions Answered to explain.

He quotes Tim Keller’s “The Reason for God” so:

The report of Jesus’s resurrection would have also have been unthinkable to the Jews. Unlike the Greeks, the Jews saw the material and physical world as good. Death was not seen as liberation from the material world but as a tragedy. By Jesus’s day many Jews had come to hope that some day in the future there would be a bodily resurrection of all the righteous, when God renewed the entire world and removed all suffering and death.  The resurrection, however, was merely one part of the complete renewal of the whole world, according to Jewish teaching. The idea of an individual being resurrected, in the middle of history, while the rest of the world continued on burdened by sickness, decay, and death, was inconceivable.

[…]If someone had said to any first-century Jew, “So-and-so has been resurrected from the dead!” the response would be, “Are you crazy? How could that be? Has disease and death ended? Is true justice established in the world? Has the wolf lain down with the lamb? Ridiculous!” The very idea of an individual resurrection would have been as impossible to imagine to a Jew as to a Greek.

And there’s more in a second post (this is Keller quoting N.T. Wright):

Over the years, skeptics about the resurrection have proposed that the followers of Jesus may have had hallucinations, that they may have imagined him appearing to them and speaking to them. This assumes that their master’s resurrection was imaginable for his Jewish followers, that it was an option in their worldview. It was not.

Others have put forth the conspiracy theory, that the disciples stole the body and claimed he was alive to others. This assumes that the disciples would expect other Jews to be open to the belief that an individual could be raised from the dead. But none of this is possible. The people of that time would have considered a bodily resurrection to be as impossible as the people of our own time, though for different reasons.

Another reason to question whether the concept of resurrection could be applied to Jesus is because there is no expectation that the Messiah was even supposed to die, much less be resurrected.

Dr. William Lane Craig explains:

The original disciples believed that Jesus was risen from the dead despite almost every predisposition to the contrary. Three aspects of the disciples’ disposition following Jesus’s crucifixion put a question mark behind the faith and hope they had placed in Jesus:

1. Jesus was dead, and Jews had no anticipation of a dying, much less rising, Messiah.
2. According to Jewish law, Jesus’s execution as a criminal showed him out to be a heretic, a man literally under the curse of God.
3. Jewish beliefs about the afterlife precluded anyone’s rising from the dead before the general, eschatological resurrection of the dead.

It is important to appreciate, with respect to the first aspect of their situation, that in Jewish expectation Messiah would conquer Israel’s enemies and restore the throne of David, not be shamefully executed by them. Jesus’s ignominious execution at the hands of Rome was as decisive a disproof as anything could be to a first century Jew that Jesus was not Israel’s awaited Messiah, but another failed pretender. Failed Messianic movements were nothing new in Judaism, and they left their followers with basically two alternatives: either go home or else find a new Messiah. These were no doubt hard choices, but nevertheless they were the choices one had. After surveying such failed Messianic movements before and after Jesus, N. T. Wright remarks,

So far as we know, all the followers of these first century Messianic movements were fanatically committed to the cause. They, if anybody, might be expected to suffer from this blessed twentieth century disease called ‘cognitive dissonance’ when their expectations failed to materialize. But in no case, right across the century before Jesus and the century after him, do we hear of any Jewish group saying that their executed leader had been raised from the dead and he really was the Messiah after all.

And here’s more support for the no individual resurrection point:

Finally, Jewish hope in the resurrection of the dead was invariably a corporate and eschatological hope. The resurrection of all the righteous dead would take place after God had brought the world as we know it to an end. Surveying the Jewish literature, Joachim Jeremias concluded,

Ancient Judaism did not know of an anticipated resurrection as an event of history. Nowhere does one find in the literature anything comparable to the resurrection of Jesus. Certainly resurrections of the dead were known, but these always concerned resuscitations, the return to the earthly life. In no place in the later Judaic literature does it concern a resurrection to d o x aas an event of history.41

Even if the disciples’ faith in Jesus had somehow managed to survive the crucifixion, they would at most have looked forward to their reunion with him at the final resurrection and would perhaps have preserved his tomb as a shrine, where Jesus’s bones might rest until the eschatological resurrection. That was the Jewish hope.

But we know that that did not happen. Despite their having most every predisposition to the contrary, it is an indisputable fact that the earliest disciples suddenly and sincerely came to believe that God had raised Jesus of Nazareth from the dead.

So I hope that enough has been said there for you to realize that talking about resurrection with respect to Jesus is a very weird thing for the early church to do – that is, unless it actually happened.