1 Corinthians 15:5

And that he was seen of Cephas, then of the twelve:

The verse names Cephas and then the twelve as eyewitnesses who saw Christ after He rose, giving evidence and testimony to His resurrection. It belongs to what was delivered first of all as received: that Christ died for sins according to the Scriptures, was buried, and rose again according to the Scriptures. After Cephas and then the twelve, He was seen by above five hundred brethren at once, of whom the greater part were still living and some had fallen asleep, then by James, then by all the apostles, then last by Paul as one born out of due time.

The verse records part of the oft-repeated appearances of Jesus to His disciples after His resurrection. Cephas is Simon Peter, and his assured testimony about encountering the risen Jesus carried weight with the disciples and helped revive their faith while it still struggled against doubt. Jesus showed Himself to His sorrowing, heart-broken disciples at the same time the saints raised with Him were appearing to many, and His appearing dispelled their fears and gave them gladness and joy.

Those repeated appearances, together with the appearances of the dead who were raised with Jesus, gave accumulating evidence that Jesus truly rose from the dead and is the divine Son of God. That evidence exposed the lie that the disciples stole the body and planted the truth in the minds of those willing to believe. His death, resurrection, and appearances in person, followed by His ascension to the Father, establish for believers the resurrection of the dead and the future immortal life of the just. Paul saw and spoke with the same Christ who was crucified, risen, and ascended, alongside Cephas, James, John, and the other disciples, and his sight and conversation with the risen Jesus gave him a testimony as real and of the same kind as theirs, though he had not seen Jesus during His earthly life.