My speech and my preaching were not with persuasive words of human wisdom, but in demonstration of the Spirit and of power. (1 Corinthians 2:4)
To attain simplicity in preaching is of the utmost importance to every minister who wishes to be useful to souls. Unless you are simple in your sermons, you will never be understood, and unless you are understood, you cannot do good to those who hear you. Of course, the first objective of a minister should be to preach the truth, the whole truth, and nothing but the truth as it is in Jesus. But the next thing he ought to aim at is for his sermon to be understood, and it will not be understood by most of his congregation if it is not simple.
To attain simplicity in preaching is by no means an easy matter. I fear a vast proportion of what we preach is not understood by our listeners anymore than if it were Greek. When people hear a simple sermon or read a simple tract, they are apt to say, "How true! How plain! How easy to understand!" and might assume that anyone can write in that style, but are unaware of the diligence required to maintain simplicity.
Simplicity in preaching is not childish preaching. If we suppose that the people like that sort of sermon, we are greatly mistaken. If our listeners get the impression that we consider them a parcel of ignorant folks for whom any kind of "infant's food" is good enough, our chance of doing good is lost altogether. People do not like even the appearance of condescending preaching. They feel we are not treating them as equals, but as inferiors. Human nature always dislikes that. They will at once put up their backs, stop their ears, and take offense.
Finally, coarse or vulgar preaching is not needed. It is quite possible to be simple and yet to speak like a gentleman with the demeanor of a courteous and refined person. It is an utter mistake to imagine that uneducated and illiterate men and women prefer to be spoken to in an illiterate way by an uneducated person. As a rule, people, no matter their position in society, only tolerate vulgarity and coarseness in the pulpit when they can get nothing else.