Role playing is when you pretend as if you were a certain person. It is similar to a skit, except that it is unscripted. You might think of it as the "reality show" version of a skit. The role players should each be assigned a role, and then the facilitator will set the scene. Once this is done, the role players take over and act as they think the person they are playing would act. The facilitator should probably also adopt a role so that the group can be kept on track without taking them out of the experience.
Before you start, explain to the Pathfinders that they must act as they think the person they are playing would behave. Emphasize this especially to the ones who are assigned the role of an antagonist (i.e., a Pharisee or a Philistine). The natural tendency is for the Pathfinder to change the outcome by "converting the sinner." You might try assigning the "bad guy" roles to your more outgoing Pathfinders, and assigning the "hero" roles to the more introspective members of your group.
Choose a scene that fits the number of Pathfinders involved so that everyone can be included. If you are doing this for an audience, use them as the "crowd" (if there is one) rather than assigning several kids to this role. Ignoring this advice will almost certainly result in suboptimal participation, and an unsatisfying experience for the role players assigned "crowd" roles. If your group is too large to avoid the "crowd" problem, split them into smaller groups and assign them different "scenes" for role playing.