The apostle Paul never hesitates to assert his authority. His authority rests on two pillars: God's Word and God's calling. He says that God entrusted him with "the proclamation." Then he says he was entrusted with this proclamation "according to the commandment of God our Savior."
This "proclamation" is connected with his office. He is a public herald, an official representative of the King. His message is the King's message. It is a public message, a message to be cried out from the roof tops and street corners. It is most certainly not a secret message for the initiated, not a private message to be enjoyed within the fellowship of believers only. It is a message to be declared as far and wide as the King's realm extends—to the ends of the earth. It carries with it the universal authority of our Lord Jesus Christ (Matthew 28:18-20).
And Paul did not choose this office of public herald. It was bestowed on him "according to the commandment of God." To be sure, it is a great honor. But, "No one takes the honor to himself, but receives it when he is called by God" (Hebrews 5:4). And God calls and appoints men as He sees fit, by His will and authority. John Calvin says, "He declares that it was by God's command, meaning that God did not choose him because he was the fittest and ablest, but because such was His good pleasure" (Sermons on Titus, pg. 31).
What can we learn from this?
First, if you are a pastor, the same is true of you. You have authority by virtue of God's Word and God's calling. You have been appointed as a herald. Your job is to publicly proclaim the Word of the King. Are you? Or are you apologizing for His word, shaving it down, adulterating it (2 Corinthians 4:2)? Are you a herald or a huckster, peddling the word of God for your own gain (2 Corinthians 2:7)?
Second, you didn't make yourself a herald. God did. He gave you gifts and graces. He caused a local church to recognize your gifts and character and to set you apart in the office of pastor. You did not ordain yourself. And your message is not your own—it is His word. He entrusted you with a message to preach, to proclaim, and He did this by His command. You cannot escape it, you cannot throw it off, and you dare not neglect or misuse it. You are a servant of Christ and a steward of the mysteries of God, and "it is required of stewards that one be found trustworthy" (1 Corinthians 4:1-2). Are you?
Third, if you are in fact a faithful herald, bearing the true message of the King, then you will bear the reproach of men. Are you ready for that? Remember what the apostle Paul said of himself: “For am I now seeking the favor of men, or of God? Or am I striving to please men? If I were still trying to please men, I would not be a bond-servant of Christ” (Galatians 1:10). If you can't take reproach, God has not called you. But if they hate you and reject your message, remember that they are actually rejecting God.
All of these lessons assume that you have in fact been called by God to your office. False teachers have always claimed God's authority. What audacity! Can you imagine the judgment stored up for those who claim to speak for God, but who are liars? The Lord Himself told His prophet, Jeremiah, what false heralds can expect, and it is dreadful:
Then the LORD said to me, “The prophets are prophesying falsehood in My name. I have neither sent them nor commanded them nor spoken to them; they are prophesying to you a false vision, divination, futility and the deception of their own minds. Therefore thus says the LORD concerning the prophets who are prophesying in My name, although it was not I who sent them—yet they keep saying, ‘There will be no sword or famine in this land’—by sword and famine those prophets shall meet their end! The people also to whom they are prophesying will be thrown out into the streets of Jerusalem because of the famine and the sword; and there will be no one to bury them—neither them, nor their wives, nor their sons, nor their daughters—for I will pour out their own wickedness on them” (Jeremiah 14:14-16).