Agrippa, having lived in the area all his life, is far more familiar with Jewish traditions and would have been more familiar 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 we say and some will not. Neither Agrippa nor Festus trusted Jesus in the moment. Would one more conversation with Agrippa have made a difference? Is there some set of circumstances that would cause Festus to listen? Only God knows, but we have the responsibility to tell others of Jesus regardless of the outcome.