If you’re trying to help a friend understand the reality and significance of the resurrection, the gospels present the best insights because they place the resurrection of Jesus in the context of the life, teachings, ministry, death, and ascension of Jesus.
If your friend doesn’t believe in the resurrection, it’s because “the god of this age has blinded the minds of the unbelievers to keep them from seeing the light of the gospel of the glory of Christ” (2 Cor 4:4). The Spirit needs to awaken them to their need for Christ before they’ll be able to believe in Christ and his miracles, including the greatest miracle of all: the resurrection.
To that end, the gospels give us the best evidence of the resurrection of Jesus because they record the predictions of Jesus that he would die by crucifixion (which only the Romans could carry out) and then rise from the dead on the third day. All four gospels corroborate each other’s testimony, even though they were written at different times by different people on different continents.
Still, if your friend needs more proof of the resurrection outside the gospels, there are two pieces of evidence that are striking to me: the fate of the disciples and the explosion of the church.
1. The Fate of the Disciples
The people who spent the most time with Jesus before and after his resurrection were the disciples. And we know that all 12 disciples suffered brutal persecution to the point of violently untimely deaths (excluding John). And all because of their unshakable commitment to the resurrection of Jesus.
Yes, people die for things they believe might be true. But nobody is willing to die for something they know is untrue. The disciples would have known better than anyone if Jesus was still in the grave (or if someone close to him stole the body out of the grave). But John suffered grueling exile proclaiming the resurrection (Rev 1:5), and the rest died proclaiming that Jesus is alive (along with many other followers like Stephen in Acts 7).
2. The Explosion of the Church
Just a few weeks after the brutal death of Jesus, Luke records that thousands of people became followers of Jesus on the Day of Pentecost in Jerusalem (Acts 2:41), all of them believing that “God has raised this Jesus; we are all witnesses of this” (Acts 2:32). Hatred and persecution of Christians was only increasing in Jerusalem during this time, as Acts 3-8 recounts. There would be no reason for these crowds of people to put their faith in Jesus other than the reality of his resurrection, and the overwhelming number of witnesses who testified to it.
The church exploded far beyond Jerusalem, to Judea and Samaria, and outermost parts of the earth just like Jesus predicted in Acts 1:8. Much of this was due to the ministry of Paul, who was a persecutor of Christians until he had his own encounter with the risen Christ (Acts 9).
No other world religion claims their founder is still alive (not reincarnated, resurrected). Christianity lives or dies on the resurrection, because it proves that the death of Christ on the cross to pay for our sins really is finished and there’s nothing more we need to do in order to be loved and redeemed by God (1 Cor 15). Praise God for all the evidence he’s given us to show us the new life we have in Christ through his resurrection!