Ministry in brief

What is ministry? What is the role of a pastor? What is the role of a leader in a christian group? How do you help in the changing of peoples lives? Questions all for thought. Recently going through my mind as i have talked with people and also watched what has happened in many different areas of ministry. Each church or group has different ideals upon which its practice is run and different groups that it works with which also affect how it targets and practices the teaching of Christ. What are the foundation principles upon which these should all reast or are they fluid?