What does John 18:23 mean?

Nobody likes to have their sin exposed (John 3:19–20). Responses usually include rage against the person who points out the wrongdoing (Proverbs 9:8; 29:9). Power tends to make people arrogant; this leads some authority figures to expect a worshipful attitude from others. That Jesus did not shrink in the face of the high priest, but dared to challenge his actions, was enough to inspire a hateful response.

Jesus has been improperly accused, without evidence, and ordered to explain Himself (John 18:19). His initial response was to declare the hypocrisy of His accusers, who already knew exactly what He was teaching (John 18:20). He also challenged them to provide evidence of wrongdoing (John 18:21). Someone nearby lost their temper and slapped Him (John 18:22).

The remark made here reiterates that Jesus' accusers have no evidence against Him. If they did, they would have been able to "bear witness about the wrong." Simply defending Himself by pointing out that there is no evidence is not worthy of assault. If there was reason to say He was guilty, it would have been given—lashing out in violence is simply more proof that the accusers have no rational case against Jesus.