Called for Ministry?

When people speak of calling, what do they mean, especially in the context of ministry? This seems to be a topic often brought to the forefront here at seminary. Do you have a call? What are you called to do? When or how were you called? But I ask, where did this idea of calling originate, at least in the way we understand and use it today?

Calling is a popular term used often in relation to the Reformed Tradition or Calvinism. Isaac Backus was especially important to the development of the inner calling that one receives from God to preach the Gospel. Backus was fighting an oppresive system, none but the educated could preach...even if they were unregenerate and wicked men. Backus and the New Lights were driven by thier pietistic faith to defend the inner call for ministry.

Calling then and now seems to be a justification for authority. In any heirarchical style of leadership, one is called over the congregation to lead its affairs, thus authority must be established. Something I value, which I have had too little experience with, is flat leadership. In flat leadership, some are called as apostles, teachers, prophets, preachers, etc, but none are called over the congregation, rather all are called for the congregation. Everyone builds the body, not just one or two. Calling seems to be a modern linguistic trick to preserve power for the top of the ladder in the church whether that be a pope or a pastor.

Another thought, can anyone be called without a a church calling them? I can say that God has called me to preach, but until a congregation calls me then am I really called?