This removes all doubt that the followers of Jesus could have stolen His body. The enemies of Jesus became a their own witness that Jesus literally rose from the dead.
The guards told the chief priests everything that happened at the tomb. This means that they had a complete account of the earthquake, the angels rolling away the stone, and the angels giving the message to the women that Jesus was alive from the dead. They may have even seen Jesus walk out of the tomb.
The very ones that the Jews had secured to guarantee there would be no rumors of Jesus being raised from the dead, became the first witnesses of it. Yet, with the testimony of impartial, non-religious eyewitnesses, they chose not to believe (Luke 16:31).