Agrippa, having lived in the area all his life, is far more familiar with Jewish traditions and with this new movement of followers of Jesus. Agrippa listens to Paul’s story with great interest, but Festus apparently thinks Paul is just a religious fanatic.
When we tell others of our relationship with Jesus, some will be open to what is being said and some will not. Neither trusted Jesus in the moment. Would one more conversation with Agrippa have made a difference? Is there some set of circumstance that would cause Festus to listen? Only God knows, but we have the responsibility to tell others of Jesus regardless of the outcome.