Persecution, when intense and prolonged tends to weaken the persecuted. What is needed at that time is encouragement and strength to continue with renewed vigour. At such a time a personal testimony (which is a personal experience/knowledge) from one who has endured and overcome similar persecution provides the encouragement and motivation to continue holding on or simply stand up to the persecution.
Jesus is the one who is our Hope. He is the one for whom we are willing to go the end of our everything because He has done it for us first. He has promised that there will be an end to the persecution and that end will be victory. So when Jesus testifies, His testimony gives us the necessary courage to gird up and continue to press on till He comes again to keep up His promise.
We are afraid to be clear witnesses in a culture where we aren't persecuted due to the fear of rejection, the pressure of popular culture and mainly the absence of a deep personal and intimate relationship and experience with Jesus. Most of us have just skimmed the surface of our relationship with Him. Unlike those who were with Him when He walked the face of this earth, our knowledge of Him is more head-knowledge than heart knowledge.
For eg. If I was blind like Bartimaeus and had been given my sight back I would be compelled to be a clear witness to what I had experienced. The fear of man etc would be overruled by my own experience. No one would be able to stand up/say anything against what I had received.
This intimate awareness is available to us even today even though Jesus is not physically with us and I believe that those of us who have reached out and availed of this are clear witnesses in the areas of their experiences.