This is a pretty accepted historical fact, even among some skeptics. Why? Because there isn’t a single instance of anyone hostile to Christianity in the first century telling people to go check out the body. The Jewish leaders’ first response in the months after the resurrection wasn’t, “Uh, guys, these ‘apostles’ are crazy. Jesus’ body is in the tomb right where it was put. Go see. It’s like a block from here.” No, there response instead was, “Well, Jesus’ friends stole the body.” Meaning they were trying to come up with an explanation as to why the tomb was empty. And they sure as heck weren’t going to tell people what the guards saw… Also, there isn’t much of a record of anyone, Christian or not, showing any interest in the tomb Jesus was put in in the first few centuries. No anti-Christian claimed Jesus’ un-resurrected body was still in there and no Christian treated it as a shrine where Jesus’ body had spent considerable time. It was just simply accepted as fact among those who hated Christianity and those who followed it that Jesus’ body had only been in it for a few days.
2) The apostles were willingly persecuted for believing Jesus had been raised from the dead.
“But people die for religions all the time!” Maybe they do, but not people who are in a position to know from their own eyes whether the claim they’re dying for is true or false. Would Peter have allowed himself to be flogged and jailed and eventually killed for something he hallucinated? And how would his hallucination explain the empty tomb? Did he steal the body from the tomb, forget about it, hallucinate the resurrected Jesus, and then believe the hallucination to the point of death? Or perhaps he was lying. You know, to get money and power. Except that then you would have to say he made up a lie for money and power which he then stuck to through a life of persecution and beatings and poverty and eventual martyrdom. And you’d have to say that John went along with him. And Jesus’ brother (who hadn’t believed in Jesus before the crucifixion and resurrection). And James and Thomas. And the other disciples. And about 500 other people according to 1 Corinthians 15. They all cooked up a lie and were willing to die for the lie even though they knew it was a lie. No, they didn’t hallucinate it because hallucinations don’t cause tombs to empty, and they don’t appear to 500 people. And they weren’t lying because liars for money or power don’t make good martyrs. Translation: these apostles really saw Jesus raised from the dead, and that’s why they were willing to die for it.
3) He said it would happen.
The disciples rarely, if ever, got it, but Jesus repeatedly said He would die for sins and then be raised from the dead. From saying the Jews could destroy “the temple” and He’d raise it up after 3 days to comparing Himself to Jonah who spent 3 days in the belly of the fish, Jesus made it known prophetically that He was going to die and be resurrected to save people lost in their sins. You can deny these sayings in the Gospels if you so choose, but the best historical evidence we have of Jesus of Nazareth (Matthew, Mark, Luke, and John) say that He predicted His own death and resurrection, and that His conscious knowledge of His coming crucifixion was why He was in Jerusalem on the Passover when Jewish leaders arrested Him.
4) His Gospel is believed, and His church has not disappeared from the Earth.
Jesus said His followers would be His witnesses to the ends of the Earth. That has been going on since the 30s A.D., and it hasn’t ever stopped. Despite flaws and errors and disagreements and dark spots, followers of Jesus Christ have gone about telling others about Him for a period of time roughly equivalent to the entire lifespan of the United States 8 times over. They’ve been doing just what He said they would, specifically in Matthew 28 and Acts 1. His true, believing followers say that He is alive just like the Bible says He is, and they continue to share that message (and what His death and resurrection mean for sinners) with unbelievers. Just as Christ said, the gates of Hell have not prevailed against His church. His people. His bride. He intercedes for them. He is their Head. The Bible says that Jesus is alive, and for those of us who trust in Him, He is our King and mediator now.
The tomb was empty. The apostles died for the Savior they saw raised from the dead. Jesus did what He said He would. And He is still in charge of the church, alive as ever and at the right hand of the Father, running the show. Jesus Christ of Nazareth is alive.
And that is why His promise is still kept.
Dead men don’t keep promises.