Dr. Charles L. Feinberg (world-renown OT scholar; a seminary prof who told John MacArthur that he missed the whole point in the passage when Dr. MacArthur was just a seminarian) on prophetic (preaching) ministry:
Just as surely as there is fear when the lion roars, then, there must be prophesying when the Lord Jehovah speaks. The prophet cannot but prophesy. He must obey God no matter how the people react to his message. Amos prophesied, as did all the prophets of God, because he was impelled by divine constraint to do it. What surer authority did the prophet need? None, because he had the authority for his message from the omnipotent God Himself [The Minor Prophets (Chicago: Moody Press, 1990), 96].
For those of you that are preaching this weekend, preach the Word!