I think all three are operative. Leaders provide direction and meaning through immediate dictate or personal example. The leader's audience is seeking leadership out of a combination of fear and hope and a desire for acceptance: they are influenced when a leader increases hope, decreases fear, and provides a meaningful role for the follower in whatever the project may be...thus, they trust the leader and submit to her direction.
Leaders offer a narrative that brings an audience into something meaningful and hopeful: their leadership is a matter of creating an identity for an audience that creates solidarity around particular values that lead to prescribed actions.
The leader's narrative is suited to the task at hand: mobilizing a crew to unload a truck, motivating a political party to endorse a divisive platform, energizing a classroom of students to complete a difficult task, or getting a group of volunteers to participate in a provocative experiment.
Leaders will encourage sacrifice for the greater cause, often using themselves as personal examples, or by threat of punishment: the punishment can be dismissal from the team, stigma and peer pressure, or physical assault.
So what is the greater cause to which these volunteers are working towards?