It also raised him from the grave. Paul supported his testimony of Jesus' resurrection by listing many of its eyewitnesses. That appearance forever changed Paul's life. It should forever change ours. Nothing before or since has been as historically important as the resurrection of our Lord.
All eternity hinges on that event.
Paul understood that one cannot abandon the doctrine of Jesus' bodily resurrection without also abandoning the faith. More than that, we are then found to be false witnesses about God. Then those also who have fallen asleep in Christ are lost. In Christ all will be made alive. As Paul concluded his letter, he did not realize how important his words would become.