If we truly believe that our souls are saved and that we need to share that truth with others in the world, we should probably share the joy that comes with it. Having that peace that Jesus describes means maintaining our attitude through good & bad times-that we are consistent in our joy. Kind of hard to convince others of the right way of life if we don't act like we believe it either.
"Rejoice. And again I say-rejoice." Philippians 4:4