To be a Christian is to believe we are commanded and authorised to say certain things to the world; to say things that will make disciples of all nations. ↗
Here's the simplest answer: Within weeks, the disciples proclaimed the resurrection of Jesus Christ, that He had been bodily raised from the dead and appeared to them. ↗
The first thing that stuck in the minds of the disciples was not the empty tomb, but rather the empty grave clothes - undisturbed in form and position. ↗