To act as a representative of God, one must be called of God. Having multiple representatives all teaching conflicting messages wouldn't make sense. And yet that is what we see today. Ministers from all sects and creeds claim authority, sometimes explicitly, but often implicitly.
Real authority is not something that can be bought. Authority is the Lord's to bestow. The authority of God not only permits a man to preach the Gospel, but it allows him to have direct revelation from God for the person or people he is called to serve--just as Moses or Enoch did. It also allows a man to act in the name of God--to do works that only God Himself can do, except that He delegates this authority to that man.