A witness is someone who can verify an activity and is able to give an account of what happened becasue they were present when the activity happened. A church facing intense persecution would be more apt to respond to someone who has been persecuted themselves and and have overcome. Jesus is a faithful witness because, after enduring persecution and death, he can testify to the fact that God is, the great I Am, and is able to save your souls. Jesus, who was once dead, is now alive and sitting on the right hand of his Father, waitng for His Church, the faithful believers to join Him in paradise. Jesus is the only One who can testify to this, he is the one true Witness and He has given His testimony concerning God's plan for our ressurection and eternal life. We can be encouraged that Jesus, who was once dead, but now lives, has taken on our sins so that we too, although we must die, will again live with Him forever in eternity. We should be encouraged.
As for "why we are afraid to be clear witnesses in a culture where we aren't persecuted?" I can only suspect that our fears stem from a lack of faith concerning our beliefs that God is who He says He is. We are comfortable in our skin right now and our minds and our hearts are not directed at God.