As the disciples went out on mission, without Jesus for the first time (Matthew 10:1-16), He explained the dangers which they would face after He had gone back into heaven.  In the same way that Jesus would be arrested and beaten, so would they (John 16:1-4).  But, despite their suffering (John 16:33) they must not step back from the mission of making Christ known.
 
The hostility which believers would face was not because of themselves, but because they identified with Jesus: the Son of God, the Creator of the universe, the King of kings and Lord of lords (John 15:18-21).  People who want to have control over others, would feel threatened by any superior ruler, and especially God.  Like Saul before his conversion, they would want to punish anybody who submitted to Jesus (Acts 22:1-5), encouraging other people to do the same (Acts 8:1).
 
However, the disciples should not worry about what to say or how to defend themselves.  God would personally put the right ideas into their heads and the right words into their mouths, as He did with Daniel’s friends (Daniel 3:16-18).  The Lord would enable them to speak the truth about Jesus, and their relationship with Him.  Under Roman law they had a right to speak in their own defence, and God would use that opportunity to announce the gospel to the top authorities (as the Apostle Paul did in Acts chapters 21-26), so that the leaders in society might hear the truth about Jesus - and some were converted.
 
Whenever you are asked to explain your Christian faith, do so clearly and gently.  Be ready to speak - not in your own defence but to proclaim Jesus (1 Peter 3:18).  And yet fear is very common; it holds us back from ministry and mission.  Fear is one of Satan's tools to stop us.  But the Holy Spirit is given to make us bold to speak up about Jesus (Acts 1:8), so there is no reason to be afraid.  The Spirit is always with us and always knows the best thing to say about Christ to the people around us.  Trust Him.  Let Him inspire you and shape your words with potent truth (Isaiah 49:2).  However high the accusation against a believer goes, that is where God is determined that the truth about Christ should be heard.