Like the Wizard of Oz who appeared to be bigger than life but, in reality,
was just a man with a microphone standing behind a curtain, pastors are also
just men. They are really no different from any other human men we all
know. They're not smarter, faster, stronger, more charming or better in
any way than butchers, bakers, or candlestick makers. Pastors do hold a unique office in God's kingdom. They are called and ordained servants of the Word and set aside deliver God's gifts to us. They're divine delivery men. Their office, like the UPS man or the pizza guy, has an identifiable uniform. A uniform denotes a certain respect for a vocation's office, and authority that it carries. For example, we would be happy to accept a package from a man dressed in brown shirt and shorts, but might question receiving a package from a shady character wearing aviator sunglasses and a hooded sweatshirt. The trustworthiness of the vocation being fulfilled is shown by the uniform - the person who wears it is essentially unimportant and interchangeable with any other person who is set aside to wear it.
Their authority to preach and teach God's Word as a called and ordained servant of that Word and by His authority is in the office they have been given. And that office of pastor, like any other vocation, exists authoritatively only in a specific relationship - to his own congregation. A pizza guy doesn't have any authority to deliver free, all-you-can-eat pizzas to his friends and family just because it is his job to deliver pizzas. He doesn't get to choose whom he is called to serve with his vocation. He doesn't get to choose what toppings you get on the pizza he delivers to you. Like a pastor, he passes on to us what he has received, and what he has been set aside to deliver to us.
However, pastors are servants of the Word as well. The Word of God is authoritative and powerful independent of the pastors who proclaim it. It creates faith (Romans 10:17), it is what makes Sacraments sacraments. "Baptism is not simple water only, but it is the water comprehended in God's command and connected with God's Word," and "It is not the water indeed that does them, but the word of God which is in and with the water, and faith, which trusts such word of God in the water. For without the word of God the water is simple water and no baptism. But with the word of God it is a baptism." (Small Catechism). Note that it does not say that it is the water comprehended in God's command and connected with God's Word when spoken only by the pastor.
God's
Word is authoritative simply because it is God's Word and accomplishes what He
sets out for it, regardless of the delivery method He chooses in any given
situation - whether it is a layman, a donkey, a pastor, a burning bush, or an
unbeliever. It is the Holy Spirit working in that Word that accomplishes
God's will, not the Office in and of itself since the Office does not properly
exist except in service to deliver that Word. That is why we can trust
that even the Word preached and Sacraments administered by an unbeliever in the
Office is still God's Word and as sure as if Christ Himself preached it.
God's Word is living and active, it does what it says. "The Word...does not
become false because of the person or his unbelief," (FC SD IX:25).Pastors, because of the authority of the Word that they deliver through their office, need to be careful that they do not fall prey to the temptation of believing in their own self-importance. The pay isn't usually very good, but the authority with which many members revere him sure is a nice perk. The pomp and circumstance with which he carries out the service, often wearing all sorts of fancy liturgical bling adds to the effect - and the temptation. It's easy to see how some may be begin to think that God's Word proclaimed from their lips is more powerful and authoritative than that same word is from the lips of a mere layman.