What, then, are the priests and bishops? Answer: Their government is not a matter of authority or power, but a service and an office, for they are neither higher nor better than other Christians. Therefore, they should impose no law or decree on others without their consent. Their ruling is rather nothing more than the inculcating of God’s word, by which they guide Christians and overcome heresy. As we have said, Christians can be ruled by nothing except God’s word, for Christians must be ruled in faith, not with outward works. Faith, however, can come through no word of man, but only through the word of God, as Paul says in Romans 10[:17], “Faith comes through hearing, and hearing through the word of God.” Those who do not believe are not Christians, they do not belong to Christ’s kingdom, but to the worldly kingdom where they are constrained and governed by outward rule. Christians do every good thing of their own accord and without constraint, and find God’s word alone sufficient for them.

– Martin Luther, Temporal Authority: To What Extent It Should Be Obeyed, in Martin Luther’s Basic Theological Writings, ed. Timothy Lull, pg. 691-692

Question:

In what ways to those with positions of authority in the church (pastors, etc.) turn their office into a position of power rather than of service?  Is there a difference between power and authority?