In the world of theater, actors are given a script they can memorize and rehearse before they go out to perform. But when an actor is asked to be part of improv, they must make up their script in the moment, as they go. The improv takes a certain amount of faith, knowing that the reaction from the audience (and the fellow performers) can be unexpected. In a similar way, evangelizing with people out in the world requires a level of faith and trust in the Holy Spirit (improv) as opposed to something practiced or rehearsed (a script).