If Jesus rose from the dead, then Christianity is true.
Did he not die on the cross?
All historical accounts affirm he died. He was crucified & stabbed; unlikely to survive. Pilate verified he died. No one at the time disputed he died.
Did someone steal his body?
The location of the tomb was well-known, a huge stone was rolled in front, it had a Roman seal, a unit of Roman soldiers was guarding it, and the city was overflowing with Passover pilgrims who would've been witnesses. If the guards failed, they would've been executed. Bribery would've led to failure and execution. Neither the Romans nor Jewish leaders wanted the body to be tampered with for political reasons. The disciples had no convincing reason to steal and defile the body of their teacher while also breaking Jewish religious law. The gospels embarrassingly admit women, whose testimony was seen as worthless in that era, first told the apostles about the empty tomb, which is a horrible way to invent a story to convince people, so it shows honesty. Even today, getting rid of a dead body with no trace is challenging.
What if people hallucinated Jesus resurrected?
It's inconceivable that hundreds of people of average soundness of mind should experience all sorts of prolonged sensuous impressions and that all these experiences should rest entirely upon hallucination.
Is it a legend?
Legends don't develop while eyewitnesses are alive to refute them, but a creed mentioning the resurrection existed within only a few years. Legends aren't supported by external history and archaeology. The legend theory doesn't explain the sudden courage of the apostles, who were scared, denied they knew Jesus, and hid, nor their bold preaching of his resurrection until torture and death. Even the Talmud by Jesus' enemies says he was a real man who was killed for sorcery. Virtually all historians agree Jesus was a real man and reject that he was a mythological figure.
So, he likely resurrected.
https://youtu.be/A0iDNLxmWVM 