Just as the ambassador from England represents his king, we as ambassadors of Christ representing our King of Kings and Lord of Lords. And as an ambassador he proclaims the message of his king with the authority of his government behind him, so we are to preach, to proclaim the message of our King with the authority of His Word behind us. And as a herald of his king, he is to preach. The Word of his King Paul commanded Timothy to preach the Word. A preacher has only one message to proclaim, the message that God has given in His Word, namely, the gospel, the good news of God.
Preachers are to cry aloud in clarion notes the good news of salvation.
The business of the preacher is to preach the Word, not book reviews, not philosophy, not science or current topics of the day. To preach the Word is to warn people to flee from the wrath of God that will be poured without mixture on all the ungodly and unsaved. It is to tell them of a hell to be saved from and a heaven to be saved to and the blood of Jesus Christ to be saved with. To preach the Word is to preach Christ. It's the exception to find one preaching a message like this today.