We believe that Jesus is alive today.
There are two main grounds for believing that Jesus of Nazareth, a man crucified nearly two thousand years ago, is alive today. These are:
The evidence that Jesus was raised from the dead is quite amazingly good. Various people have tried to prove that the resurrection never happened, and have ended up being convinced by the evidence that it is true after all.
Many Christians will use their experience as grounds for believing the resurrection. "I know He is alive - I was talking with Him only this morning." While this experience on its own may not seem too convincing to someone who does not believe, when combined with the objective grounds mentioned above it makes an even more convincing case. Not only does the historic record point to the truth of the resurrection, but we also have the testimony of many witnesses today.
One point to make is that the resurrection was not simply the re-animation of a dead body. Lazarus, in the gospel record, was brought back from the dead, he lived a bit longer, and then (we can be sure) he died. Resurrection may look similar, but it is quite different, which is why we believe not only that Jesus came back to life on Easter Sunday, but also He is still alive today.
How can you believe such an absurd idea?
Only because the evidence for the resurrection is so strong! As I say elsewhere, I am a Christian because I lack faith. Once I looked at the facts, I found it took more faith to believe any of the alternatives on offer than to believe the resurrection.
People have come up with many alternative theories to explain what happened. The more reasonable ones include:
Firstly, Jesus was almost dead when He was put on the cross. The beating He had received was one that could kill a man, and He was so damaged by it He was unable to carry the cross all the way. Nobody survived crucifixion, and Jesus was already nearly dead before He was put on the cross.
Secondly, the Romans were professional executioners. They knew a dead body when they saw one. A soldier would be killed for failing to kill someone as ordered - it was not something that they took chances with.
Thirdly, this was a high profile political execution. Maybe, just maybe, if you are crucifying a thousand people at once, you may make one or two mistakes (although there is no evidence that they ever did, even then) - but not when the criminal is a popular leader and has been tried in front of both the Roman and Jewish authorities.
Fourthly, the evidence is that He was really dead. When the spear was pushed into His side, out came blood and water - plasma. This happens after death, when the blood has ceased to circulate, and the red cells have separated from the blood plasma.
Fifthly, the body was bound in grave cloth - like a mummy, wrapped tight - and left sealed into a cold and damp tomb. A healthy person in that situation would die of cold and thirst - it is certainly not the conditions to being about a fortunate revival from close to death.
And finally, this bleeding, cricified and stabbed body is supposed to revive in the cold and darkness, unwrap itself from the grave clothes, push away a stone that several healthy women could not move, and then convince all His followers that He was risen from the dead, more alive than ever, that He had more miraculous powers than He had ever displayed before, gave them a series of lies that would lead them to be tortured and killed, and then just disappeared. It's not just unlikely, it is totally implausible.
Why would they steal the body? What use was it to them?
Even if they had found a reason to seal the body, psychologically they could not attempt such a plan - they were afraid and defeated. They had given up.
Even if they wanted to steal the body, they could not because it was under guard.
If they did steal the body, why did they go on to convince other people He was risen (up to 500 people at a time, somehow)?
And if they had somehow convinced others that He was alive, why did they then go on to die for a belief they knew to be totally false?
At what point was the wrong person mistaken for Jesus? The traditional answer (and the only one that seems to make any sense) is that the wrong man was arrested in the darkness at the Garden of Gethsemane.
But this means that not only did the soldiers arrest the wrong man, but this (unknown) man stood his ground in an extremely Jesus-like way, convinced everyone he was really Jesus, and willingly went to die in the cruellest way the Romans could manage. Where did this incredible actor come from? And what possible motivation could he have in wanting the world to believe that Jesus was dead?
It also means that it was a real live Jesus who appeared to the women at the tomb and then the disciples, and convinced them all that the impossible had happened. He appeared in a locked room, disappeared from a meal table, convinced everyone he met that he was not alive but resurrected, and then ascended into Heaven and was never seen again. That's an impressive set of conjuring tricks. And, again, for what reason? To convince the disciples of a lie, so that in proclaiming a lie they will go out and call the human race to follow the truth?
Can you supply a single example of mass hallucination that bears any resemblance to the gospel record? Or any example of wishful thinking that can be compared in any significant way with this series of events?
If the resurrection stories are a result of mass-hallucination or wishful thinking, it is a strange psychological phenomenon so unlike any other ever recorded that you really need to propose some unique cause to justify this unique effect. You might as well posit a unique encounter with a risen Lord.