It Cannot Return to Him Void
'You must also believe in the power of that message to save people. You may have heard the story of one of our first students, who came to me, and said, "I have been preaching now for some months, and I do not think I have had a single conversion." I said to him, "And do you expect that the Lord is going to bless you and save souls every time you open your mouth?" "No, sir," he replied. "Well, then," I said, "that is why you do not get souls saved. If you had believed, the Lord would have given the blessing." I had caught him very nicely; but many others would have answered me in just the same way as he did. They tremblingly believe that it is possible, by some strange mysterious method, that once in a hundred sermons God might win a quarter of a soul. They have hardly enough faith to keep them standing upright in their boots; how can they expect God to bless them? I like to go to the pulpit feeling, "This is God's Word that I am going to deliver in His name; it cannot return to Him void; I have asked His blessing upon it, and He is bound to give it, and His purposes will be answered, whether my message is a savour of life unto life, or of death unto death to those who hear it."'
(C.H. Spurgeon, 'Qualifications for Soul-Winning - Godward')