Jesus knew how difficult persecution would be for the apostles and the church (John 15:18-21).  They would be accused by religious or civil lawyers just because they believed that He was God in a human body, the Saviour of the world, the King of kings and the Lord of lords.  How could they deal with the anxiety and prepare themselves to face the trial? (Luke 12:11-12)  His instruction was simple: decide before the crisis not to worry: believe that the necessary wisdom would be given just at the right time; trust that God-given words would come to mind when needed.

They were to accept the inevitability of persecution (2 Timothy 3:12), and determine not to be afraid (Philippians 4:6).  They needed to understand that they did not need to defend their faith in Christ and the gospel, any more than a lion needs defending ... it just needs to be released and it will defend itself!  They were to rely on God giving them empowered words of gospel truth to defend them personally and attack the gates of hell (Matthew 16:18).  

That was what happened to the Apostles Peter and John (Acts 4:1-22).  In prayer they said, "Now, Lord, consider their threats and enable your servants to speak your word with great boldness." (Acts 4:29).  So threats made them even bolder in the Lord!   Stephen proclaimed Christ before the Sanhedrin court and was punished by vicious stoning, but he was rewarded by being personally welcomed into heaven by Jesus (Acts 7:54-60).  Trouble did not deter the Apostle Paul either (2 Corinthians 11:23-28) and just before his death testified that Jesus stood beside Him (2 Timothy 4:16-18).    

Inspired words still come packaged with Divine wisdom, to believers who have made up their minds not to be intimidated by the threat of harm.  That is a supernatural response to a supernatural promise.  Like soldiers in training, who know they will be fired upon and yet must not be afraid, the follower of Christ must understand that opposition will come to all who respond to the call to be a disciple.  But first, fear must be dealt with in principle (Joshua 1:9), by deciding not to accept the temptation to worry, and by believing that the Lord will give the necessary wisdom to be a good witness.