And how shall they preach, except they be sent?  – Romans 10:15

A man who goes to tell others about Christ must feel that he is sent to do it, or he will never do it properly and effectively. The man who is sent, first of all, has a message given to him. You do not say to your servant, “You go north, south, east, west, and that is all.” No, if you send him, you give him a message: “Go and say to Mr. So-and-so, this and that;” or you write it down, and you say, “Deliver that letter to such a person.” You do not leave him to go and say whatever he likes: “John, I want you to call on Mr. So-and-so tomorrow morning, and to say whatever first comes into your head.” You do not act like that, do you? Yet that is the notion some people have, nowadays, of what a preacher is; he is a man who makes his message up as he goes along; he is a “thinker;” he excogitates the Gospel out of his own brains. I have heard of a German who is said to have constructed a camel out of his own consciousness. Very likely; but I am sure that nobody will construct the Gospel that way. He must receive it by the revelation of God. The other plan is not Paul’s notion, for he asks, “How shall they preach, except they be sent?” First, then, get your message, be determined to know nothing among men but what the Lord Himself has revealed to you in His Word, by the teaching of His Spirit. Get it well into you; say to yourself, “What I am going to speak is nothing of my own; else it would fall flat and powerless; but I am going with, ‘Thus saith the Lord.’ This is God’s message.” Then, if you are sent, you will preach, and you will so preach that men will hear; and they will so hear that they will believe; and they will so believe that they will be saved. But you must go as a God-sent man, having received your message from the mouth of your Master. ~ C.H. Spurgeon

https://www.blueletterbible.org/comm/spurgeon_charles/sermons/2327.cfm