The profound significance of Christ’s resurrection comes from the threefold justification it provides: it justifies the sinner, the sinner’s hope, and God himself.
The death and resurrection did indeed really happen. They are accomplished historical facts, and by them, so too is the forgiveness of our sins and justification before God.
The opponents of Father Brown thought that debunking the fake resurrection of Father Brown would discredit the good news of Christ's resurrection. The truth, however, is the other way around.